Here are a few ideas:
1. Read the rule book. I dont mean "become a rule book official," but a working knowledge of the rules will give you confidence and confidence will help your game. See below for more about the rules.
2. Devour the official's manual. I mean that. Read it more than the rule book. Learn the procedures. It, too, will give you confidence. For the most part, the stuff in the official's manual is the stuff you need to truly "learn." 95% of all the basketball stuff you will see will be stuff you already know--you know what a foul is, you know what stepping out of bounds is, you know there are 4 quarters, you know all that stuff. The "funny rules" like false double fouls and whether or not a technical is directly or indirectly charged to the head coach is great if you know, but as a rookie, you will have a senior partner there to help you with that stuff. But the stuff in the official's manual is ALL NEW. Unless you have reffed before, you dont know where to be at time outs or how to administer a DQ or where to stand for the jump or which place to be. That, probably, is why clinics spend so much time on mechanics. Because that stuff is new and it is teachable. Judgement, while also deserving of instruction, is to some degree a matter of whistle time.
3. Do your homework. If you want to be good, dont just rely on the book you are give. Go do extra research. Go get Referee Magazine's excellent book Basketball Official's Guidebook Crew of Two Officials. Here is the link.
http://www.referee.com/books/books/bbbog205.htm
That book is awesome for a new official and a good resource as you go along.
4. Work on your calls. Get a buddy or a spouse. Have them shout out a foul or a violation, like "push" or "charge" or "travel." Then blow it and report it. Partner says "travel." You say "tweet," then signal open hand up, travel signal. Or partner says "push" you say "tweet" then fist up, then preliminary signal, then go report, "white, 3-2, push, sideline out of bounds." That sort of thing. I know it sounds silly, but it really helps.
5. Get out on the court. The only time you work on officiating shouldnt be when you do it live. And you dont need a fancy clinic to work on things. Just get a senior official and another junior official like yourself and go to a gym or an outside court. Have the senior official dribble the ball and the two junior guys position themselves. This helps immensely. People can say "dont work on mechanics and positioning" but if you arent in position to make the call your judgemnet really doesnt matter that much--since you couldnt see it.
6. Get a mentor. This is tied to #5 above. But there is no reason why senior guys wont want to help the young guys. Some dont but many do. Heck, show up early and I'd work with a newer official on the outside court before we even had to be there for our game. No problem.
Basically, if you go the extra mile it will show. If you think you can just show up and learn on the job, you wont develop as fast as others. Plus, some have the gift for it and some dont, but there is nothing you cant overcome with a bit of work.
And finally
7. Dont worry about advancement. The only thing you can control is being the best official you can be. That is up to you. Advancement isnt up to you, it is up to your association. And if you are doing well, you will get noticied. If you dont get moved up, that may say somethign about your association, not about you.
8. Find out how the big dogs want it done. That said, make sure you get the word from teh assignor or the seniour guys how they want things done. Then do it their way. If they want a tight 3 seconds call (which I doubt they woudl, just making a funny example based on recent threads) then call a tight 3 seconds. If they hate patent leather shoes, dont get patent leather. I'm not saying suck up. You dont have to go kiss a$$. But find out how the people in charge want things done and do it the right way.
9. Have a positive attitude and respect what reffing means to the participants. Do it because you love it. This, I think, is key. People take this seriously. It is important to all the coaches and the kids playing. Heck, some of these kids wont go to college and these games will be the stories they will tell with their buddies (in greatly exaggerated fashion) for the rest of their lives. And you are a part of that. Make your preparation and your demeanor reflect that you understand this is both serious and fun.
10. Have fun. Smile. Dont just be a robot. Dont think you are a police officer. You arent.
Good luck!!!!