>>1
Just read a lot of Japanese. Have a dictionary program open (I suggest JWPce, google it), and when you come to kanji you don't know (which will be a lot at first) copypasta them into your dictionary and look them up. After a while you will memorize them naturally. Try remembering the "on" readings of kanji, as they are the readings most often used in compounds. If you can memorize most of the readings for basic kanji, you'll be able to sound out words even if you've never seen them before. Also remember that each individual kanji has meaning, and try to remember the basic meaning behind each kanji rather than just thinking of them as sounds. I recently started taking biology in Japanese, and as such was learning the names of various cell parts and whatnot. I found that thanks to kanji, I was able to guess the meanings of a lot of terms, such as 光合成 (photosynthesis), thanks to the kanji which have the basic meanings "light", "combine", and "make".
As for writing, you just have to write a lot of Japanese, but don't worry about it too much as a lot of Japanese people suck at writing kanji too. It's the same as how English speakers rely on spellcheck too much and everyone is forgetting how to spell; everyone in Japan is so used to using cellphones and computers that they are forgetting how to write kanji by hand. If you always carry a cellphone or electronic dictionary, you can just use that to look up kanji you forget how to write when writing by hand (that's what I do). The other day I had to show a Japanese person how to write the word 使う (use), which was embarresing for him.