Exactly as the heading says - this is the time to try out new things, develop new techniques, and improve your game. If a player has trouble looping, for example, many will fall back on more successful shots in practice - and so continue to have trouble looping. Instead, use those very shots that need to be developed in practice matches so that they will eventually be developed enough to use in more important matches.
So, take a good look at where your game is, and where you want it to (realistically) be in the relatively near future. Then play that way in practice until you can do it well.
One thing that really helps when trying out new things is to find a weaker player to work on using new techniques in a game situation. For example, if you need work on looping against backspin, play games against someone, usually a weaker player, where you can serve backspin, he likely pushes it back, and you get to work on looping against backspin. If you play a strong player, he'll likely make stronger returns (flips, short pushes, or long pushes that you aren't quite ready for yet), and you won't get as much practice. (Plus, the games likely won't be competitive.) Or just play improvised games where the receiver always has to push back long, and then you both get to work on looping backspin!