Hi! I just have a few tips.
1. Serebii is your best friend.
You can use the Pokedex page to either try and go number by number on the or go route by route and try and catch every Pokémon at each location. This website works great for this too!
2. Use GTS.
Putting in your version exclusive for its counterpart will usually work. You can also ask for the starters and stuff.
3. Ask your friends!
Lots of people will be more than willing to help you out.
4. Stock up on Quick Balls.
Quick balls are great for Pokedex completion. Just chuck one at the Pokémon as soon as you find it. Buy a bunch of ultra balls as well.
5. Have a high-level false swipe user.
I’d imagine most people know this, but this is the best way to catch Pokémon. I have mine hold a smoke ball to guarantee running away.
Hope I helped!