The game starts off with three gender options: Boy, Girl, or ???. The third option is more-or-less a non-binary option for those that don't wish to stick strictly to the other two. I suggest not taking it too seriously and just pick what makes you comfortable. Anyway, once you've decided your name, it's time to start your adventure! 

Moirai 

Items: 
Potion x1 
Running Shoes (Talk to Dad after getting your Starter)
Pokédex & Pokégear (Professor Juniper gives these to you after picking your Starter) 
Pokéball x5 (Same as above) 
TM54 (After seeing 50+ Pokémon) 
TM17 (After seeing 100+ Pokémon) 
TM10 (After seeing 200+ Pokémon) 
Oval Charm (After seeing 500+ Pokémon) 
Shiny Charm (After seeing all 649 Pokémon - The hardest of all!) (Remember: You simply have to SEE the Pokémon, not own it.) 

After the initial cutscenes in your house, you'll get to meet your rivals for the first time. Basically they're whatever options you didn't pick. Grab the Potion, talk to the townsfolk if you want, then head inside the Lab to officially meet Professor Juniper. She'll step out of the way, and you can finally grab your starter! They're all just sitting around, minding their own business, so you only need to walk up to them to pick them out. Taking purely types into consideration and nothing else, Fire types have it the easiest early in the game, but will have trouble against the Elite Four (even more so if they're also Fighting). Water types will have some trouble with the first gym, but should be alright after that. Grass types will have the hardest time for most of the game (half the gyms are its weakness for one thing), but will have a major advantage against the Elite Four. Really it's up to you. Also the comments about being good at a certain stat are merely there to point out its strengths, and doesn't take things like movesets into consideration. 

(An important thing to note: Once you have all eight badges, you can come back to catch the other Starters. However, they don't respawn, so save!) 

Now that you have your Starter, you can go fight your rivals! You have to beat both of them to continue, but you'll be healed after the battle with Alex, so you should be alright. 

Alex 
Starter (Type weakness) - Lv. 5 

Emil 
Starter (Type advantage) - Lv. 5 

Pretty standard. Alex will have a Pokémon one generation after yours, while Emil will have the generation following that. So for example, if you picked Bulbasaur, Alex will have Totodile, and Emil will have Torchic. Obviously, it loops back around for later generations. So for example, if you picked Oshawott, Alex will have Charmander, and Emil will have Chikorita. If that sounds complicated, imagine coding all of that, including the alternate genders. 

You can heal at home by talking to your Dad. Other than that, you can head on down to the next section. 

Route 650 

Pokémon: 
Lv. 3-5 
Bidoof - 40%* 
Kricketot - 20%* 
Purrloin - 20% 
*Switch at night 

Items: 
Potion x1 

Trainers: 
Lass Katie - Purrloin Lv. 4 
Youngster Tom* - Bidoof Lv. 5 
*Get number after beating 

I don't think I have to tell you what to do here. If you're going to catch anything, I strongly suggest getting a Kricketot and leveling it up until it knows Bug Bite. It will make the next part MUCH easier, trust me. 

Aisa 

Items: 
Antidote x1 
Great Ball x1 (Talk to Gulpin Boy) 
Oran Berry x1 (Talk to Old Man inside) 

First towns aren't meant to be extraordinary, are they? Well, who cares. Grab your items and head east. You can't head west right now due to an eccentric scientist. 

(If you stop by the Pokémon Center, you'll notice it's two floors. The top floor is a Mart that adds more items based on how many badges you have, including TMs. Be sure to check back often!) 

Route 657 

Pokémon: 
Lv. 4-6 
Taillow - 25% 
Surskit - 25% 
Sentret - 15% 
Shinx - 15% 
Nidoran♂ - 10% 
Nidoran♀ - 10% 

Items: 
Exp. Share (Beat Mystery Trainer) 

There's plenty more to this area that's cut off by the water, but we'll get to that when the time comes. Get your Starter up to Lv. 8 if it isn't already, then talk to the guy with the Absol. 

Mystery Trainer ??? 
Absol - Lv. 8 

This isn't your ordinary Lv. 8 Absol. It has Pursuit, a STAB move. Hopefully your Starter has one too by now. If you took any of my advice this battle shouldn't be impossible, and there's always the option of simply beating it with numbers. It's seriously not as hard as it looks. On the bright side, you get an Exp. Share as an apology. 

The scientist will be done after winning this battle, which means we can move on. 

Route 651 

Pokémon: 
Lv. 5-7 
Rattata - 25%* 
Hoppip - 25% 
Poochyena - 15% 
Pikachu - 15% 
Abra - 10% 
Hoothoot - 10%* 
*Switch at night 

Items: 
Aspear Berries x2 
Parlyz Heal x1 
Potion x1 
Sam's Letter - Key Item (Interact with Pidgey) 
Super Potion (Requires Cut) 
Rare Candy (Requires Strength) 

Trainers: 
Lass Anna - Lv. 7 Taillow 
Youngster Jim - Lv. 6 Surskit, Lv. 6 Hoothoot 
Lass Sarah* - Lv. 6 Sentret, Lv. 6 Nidoran♂ 
*Get number after beating 

Player rematches involve fighting the Pokémon around 10 levels higher than when initially fought, fyi. They will also be evolved, if possible. It's good for grinding and whatnot. Anyway, be sure to get everything you can in this area, ESPECIALLY Sam's Letter. It's a very important item for a side quest, and you'll miss out on catching Pokémon if you don't do it. Abra (and others like it) doesn't need to evolve from trading. Instead they'll eventually evolve by leveling up normally.

Mischief Forest 

Pokémon: 
Lv. 6-8 
Caterpie - 20% 
Weedle - 20% 
Wurmple - 20% 
Petilil - 15% 
Cottonee - 15% 
Misdreavus - 10% 

Items: 
Tiny Mushroom x1 
XAttack x1 
Potion x1 
TM05 (Requires Cut) 
HM01 (Get from Blonde) 

Trainers: 
Grunt x2 - Lv. 8 Poochyena 

Here's an introduction to this game's baddies! Walk up to the couple for a scene, then you'll get into a battle. 

Aedus 
Pineco - Lv. 10 
Voltorb - Lv. 10 
Seedot - Lv. 10 

They all either know Self-Destruct or Explosion. I hope you weren't planning to do a Nuzlocke! If you've been training your Pokémon, you should be fine, and if you're lucky he'll let himself lose. Continue on, collect items, battle the grunt, and soon enough you'll find yourself near the end. However, you'll have to get through one more trainer first. 

(The strange rock near the TM is the Moss Rock, so come back later if you want a Leafeon.) 

Leona 
Meowth - Lv. 10 
Purrloin - Lv. 10 
Shinx - Lv. 10 

No gimmicks here, aside from the feline theme. Beat her like you did with Aedus, and you'll have cleared the area! The blonde will give her thanks and reward you with an HM, revealing her true identity in the process. Onward! 

Route 652 

Pokémon: 
Lv. 8-10 
Lotad - 25% 
Lillipup - 25% 
Starly - 15% 
Riolu - 15% 
Wooper - 10% 
Ekans - 10% 

Items: 
Pokéball x1 (Hidden) 
Repel x1 (Hidden) 
Potion x1 
Dire Hit x1 (Hiding to the right of the cut-able tree) 
Full Heal + Zinc (Require Surf) 
Old Rod (Talk to the Fisherman inside the shack) 
Pearl (Show the other Fisherman a Goldeen) 
Stardust (Show the other Fisherman a Horsea) 
Big Pearl + Hojot Ticket (Show the other Fisherman a Dratini) 

Trainers: 
School Kid Edgar - Lv. 8 Kakuna, Lv. 8 Pikachu 
School Kid Gina - Lv. 8 Metapod, Lv. 8 Riolu 
Fisherman Mick* - Lv. 5 Magikarp x3 
*Get number 

Seems there's a lot to do here. You'll notice a few things the moment you enter. First is the blank patches in the grass on the right. The hidden items are there. If you have a Pokémon with Headbutt, you can use it on them to shake out Pokémon. Since I doubt you have one at this point, we'll save that for a later section. The Fisherman on the right inside the shack is your first sidequest in the game. If you want to catch'em all, you have to do it. Fishing Pokémon are separated into two categories: Calm water and moving water. Same goes for surfing. It's always the same no matter where you are. 

Fishing Pokémon are as follows: 

Moving water 
Old rod = Magikarp (70%), Goldeen (30%) 
Good rod = Basculin (60%), Poliwag (20%), Horsea (20%) 
Super rod = Barboach (40%), Finneon (40%), Stunfisk (15%), Dratini (5%) 

Calm water 
Old rod = Luvdisc (70%), Qwilfish (30%) 
Good rod = Krabby (60%), Psyduck (20%), Tympole (20%) 
Super rod = Carvanha (40%), Chinchou (40%), Staryu (15%), Dratini (5%) 

As you can see, despite being the only Pokémon in the entire game to have a less than 10% chance encounter, fishing in either waters is fine in order to catch it. You won't get the Super rod until the 6th gym, so there's no need to rush. 

Charites 

Items: 
Great Ball x1 
XSpeed x1 
Leaf Stone (Talk to the guy to the northwest) 
Rare Candy + Max Ether (Require Surf) 
Chesto Berry (Talk to little boy inside) 

Pokémon: 
Clamperl x2 (Trade a Nidorino + Nidorina with the Preschoolers) 

The Clamperls will evolve into a Naive Huntail and a Modest Gorebyss after traded. Talking to NPCs might be helpful, you know. Once you've gotten everything you can, it's finally time to get your first badge! 

First Gym

Items: 
Soda Pop (Talk to the guy next to the entrance) 

Trainers: 
School Kid Rosie - Lv. 10 Hoppip 
Youngster Oliver - Lv. 10 Cottonee 

Gym Leader - Flora 
Liligant - Own Tempo - Oran Berry - Lvl 14 
•Growth 
•Leech Seed 
•Sleep Powder 
•Mega Drain 
Roserade - Natural Cure - Oran Berry - Lvl 15 
•Sleep Powder 
•Poison Sting 
•Grass Knot 
•Mega Drain 
Obtain TM86 - Grass Knot 

That Chesto Berry might save your life. As long as you attack with their weaknesses and stay awake, you'll have a badge in no time.