[ORAS] How to start filling National Dex?

[markings]

I am currently at 350/719 which means i have a long way to go. Can you guys share your experience from filling the national dex to get the shiny charm? I would like to know how you start with and how would you continue filling when you are at my stage. I am pretty sure asking someone to help with 350 pokemon is going to take a long time and i wouldn't want to burden someone to do that for me, that's the easy way out, whats the point of doing it then? So, guys/girls, please share your experience and method with me. Thank you!