Welcome to Buzzerbeater! It's a great manager simulation, the best of the many I've played.
Here are some things I think are useful as a brand new player:
Don't go crazy buying yourself new players until you know what skills are important for each position, and what levels you need them to be in your league.
Players who are 33 years old are more can start to see their skills decline. They can still be useful, but take this into account if you're thinking about buying these old guys.
A player's potential (i.e., allstar, superstar, MVP,etc) has absolutely no effect on how well he plays, or how fast he trains. So don't overpay for players with high potentials. For your first crop of trainees, star, allstar, and perennial allstar is enough.
If you are going to train, pick training guards, or bigs, but don't switch between both week to week. Stick to training the same guys for a few seasons straight. That will make them useful players for your team for longer. If you are going to train, it's worth it to invest in a level 4 (advanced) trainer. Your trainees will train faster that way.
Put some of your new manager bonus into expanding your arena. That will be important to give you enough income to add new playeers in the future.
To be successful in most low divisons, like USA D5, you'll need to master managing gameshape and enthusiasm. Getting good at those two things alone will get you promoted from most D5 leagues.
Read the FAQ
(144856.1), read it again, then ask questions. BB also has a great community of helpful people.