You can improve your writing in English and Hindi by first reading some texts from professionals through the internet or friends and family. Second, you can go through the online or book dictionary for new and complicated but easy-sounding words, which you can frequently use in essays, speeches, etc. Third, you can get the help of teachers and seniors. Fourth, is after trying out steps 1, 2 and 3 practice, practice, practice!
Hope I helped you! :) I've won many essay-writing competitions and these are the tips and tricks I've used! Good luck!