Basketball practice drills to help with passing can be either stand-alone drills focused on teaching a specific type of pass, or more complex drills that require players to use a variety of passes in game-type situations. Both types of drills are necessary - players need to learn fundamentals before they can put them to use, but they also need to practice using the passes in situations similar to what they will face at game time.
One thing any of your passing drills need to do is always reinforce the basic fundamental skills of passing. I know there are drills out there that focus on how to handle a poor pass - drills where you do things like throw the ball at a players feet as he is on the move, and he needs to adjust and gain control. these drills have their place, perhaps, but I would rather spend practice time focusing on improving passing skills so these situations don't occur to begin with.
If you haven't done so already, or need a refresher, check out the Passing Fundamentals page for instruction and basic passing drills that focus on how to pass properly.
Once you have had a few practice sessions focusing on the fundamentals, and really enforced proper form for each type of pass, begin introducing more complex basketball practice drills. Continue to emphasize best form and solid concentration, to build muscle memory so that, when the players are in the game, good mechanics become second-nature. But the more advanced drills will also add in some game-like aspects - players will be on the move, will be required to use different types of passes, may have to choose the type of pass to use depending on the situation thrown at them.
The Full Court Passing drill is a good transition drill from the simpler basketball passing drills that have players paired off, passing back and forth. This drill introduces movement to the passing drills, and is usually the drill I use immediately after I finish introducing basic passing skills.
Another basketball practice drill that combines basic fundamental passing skills with more complex passing drills is the Fast Break Baseball Pass drill. This essentially teaches players how to throw the baseball pass to a moving target - a player sprinting down court - and although the focus is really on proper form, it does resemble a game situation.
You can also check out a variety of drills run by a star coach that focus on helping your team grow its skills, particularly useful if you are coaching youth basketball.
Two more drills you can try are more complex than the previous drills. These are the 4 Corner Passing drill and the Diamond Passing drill. Both are good drills for teaching how to pass and receive on the move - particularly the 4 Corner Passing drill - but also require players to move in a preset, slightly complex pattern in between passes, which also serves to introduce players to the idea of strategy and offensive movement.
Remember in all these drills to constantly enforce good fundamental form. At the beginning, when you are just introducing the drills, stop the drill if you feel your players' form is falling apart. The more often these practice drills are run, the less often you will need to stop them, so long as the basic skills are enforced from the beginning.
In any basketball game, there will be many situations in which players will not be able to use proper passing form - they will need to adapt their passing style to suit the situation. But without a base of good form, they will have little control and great difficulty passing effectively. One drill that is great for teaching passing skills in game situations is the Drive n Dish drill - use it to hone passing skills on the move, in traffic - but still enforce good passing fundamentals.
Good passing form will often seem a little stilted in practice, not quite "game-like." But enforcing it in practice is much better than having to watch your players throw around-the-back passes or scoop passes out of bounds and off teammates ankles. Good form will carry over into the game and will help your players pass better and your teams win more games.
Also remember that, while these passing drills are particularly important at the beginning of your preseason, it is common for our players to fall into a lull at mid-season, and skills begin to slip. For whatever reason, I have found this more of an issue with passing than with other skills such as shooting or ballhandling. Throwing in a few basketball practice drills in mid-season practices with a focus on passing fundamentals can help reinforce those passing skills and keep your team on track.
"Fans never fall asleep at our games, because they're afraid they might get hit by a pass."
- George Raveling
Try UMass Head Coach Derek Kellogg's video package of drills