Like they said, there's really no rules to differentiate. What helped me most was that if the word ended with a vowel, I automatically went with feminine. Until I memorized the ones that weren't...btw don't force the memorization. Just keep practicing as usual. Do more than just Duo Lingo (read french news, kids books in french, rosetta stone, slow french music, etc.). Just less than 1 hour a day.
Ecrire.(sorry I dont have acces to accents) Heres a site where you can obtain the conjugation of any verb and its really easy to use, provided courtesy of our wonderful sitesurf: " www.aboyt.com/fr/vreb conjugator".... Thats ALL your conjugation issues solved. Be sure to add the word "conjugator" even though Duo in their wisdom deem it fit to leave it in black colour confusingly.