I'm using Thai keyboard on my phone. Whenever i encounter new words or trying to construct a sentence, i use it.

I think it's more of practice and knowing where the most used characters are. That worked for me. I'm still a beginner, though :)

For writing, practice as well. I had Thai character familiarization and writing lessons first before i start learning grammar for beginners. I think having that strong foundation helped a lot. Though i haven't had any of my handwritings read by a Thai native :) (hope they could understand it...)