If you want to go for melee, put points into brawl, melee, and strength. If you want a more shooter type game, put points into dex and wits. Don't put points into firearms initially--you'll find a firearms book in Santa Monica on one of the quests. Save your game, sell it to Trip, and buy it back twice. If you can only buy it once, go back to your previous save and just use the book so you don't lose the money. Just make sure to explore everywhere and talk to everyone you possibly can. You'll get a lot more quests, which will give you a lot more xp. Sometimes after you do certain quests, people will have new dialogue options for you.
Also, anything that increases your persuasion is good--it opens up a lot more dialogue options for you, and can keep you out of fights. Remember, you get xp for completing quests, not for killing everything that moves.
You can gain humanity points back if you dance in a few clubs for about 5 minutes. If you go to the dance floor, you'll eventually find a selectable dance option. Select it and just dance until it says that you've gained humanity. You can only do this once per club.