I REALLY like the IDPA classifier match as a good comprehensive test of basic skills.
Stage 3 IS the classifier. With a little bit of practice, you can shoot the first two stages with a high score (even all the headshots) but people tend to crash & burn on Stage 3.
Things to avoid:
(1.) Don't crowd your cover. Stay back an arm's length. Having some distance will make it easier to roll around the side of cover and engage the multiple targets
(2.) Don't shoot too fast. People have a tendency to go way too fast on Stage 3 and drop a bunch of hits as a result.
You can only learn from experience if you pay attention!