what's hard for me? that would be grammar... grammar .. grammar..
especially to the part involving particles
vocabulary also, but in the long run, was able to memorize it with constantly using it..
about textbook, I found some 100yen japanese practice text from level grade 1-6. there are lots of fill in the kanji and its very interesting..
also have you tried, "Minna No Nihongo" , this book has been highly recommended by lots of Japanese teachers that I know. Most of the conversations here are/can be used in daily conversations.