How can i avoid my grammatical mistakes?

ok, this is ridiculous. i read in cl 10 and i'm doing horrible grammatical errors. suppose- i should write " in the chair" not " on the chair".besides, i do sentence construction error too.i have some beautiful composition written by good authors. what i want to do is to rewrite their essays twice. i think , my brain will detect my mistakes automatically and correct it. is it a good thing to do? reading books is not helping me..