Ops88 I've been playing this game for a long time and I still forget a rule here and there. Infact I've never known anyone who knew every rule, every game. But after you've played for awhile you do get a lot of the rules as second nature. Some rules become such to the point that when a small detail in them change in a new edition you automatically incorporate the small detail. It's weird.
Have you met Deathklokk?
I know its generally frowned upon to read the books online, but if you want to learn at home, I reckon if you can get a mate to give you a hand when he starts off, the two of you can start building an army together. For example, if one of you collects one army, and another collects a different one, you could say do a battle once they're painted and do infantry versus infantry. Once they're done, you can agree a theme for the next month, and a set value of points, and then use those new units and so on and so forth.
For example, I started my Guard Squad recently.
I started with 3 Boxes of Kasrkin. I got truely demolished, as I had 2 Veteran Squads, and a Command Squad, up against Marines and Orks. However, the theme for the next month was 150pts worth of vehicles. I chose a Valkyrie. I was given a one on one tutorial about how to use those in a couple of games, where I was "learning the rules", and then got to use it in a game, up against Predators, Dreadnoughts, Falcons and all sorts.
It's a good way to get your stuff sorted as well.