First thing to do is get over your fear of the unknown. The Classifier is described completely in the IDPA rule book. Read it and visualize going through it until you are confident you know what each stage and string requires. Stage 3 doesn't lend itself to dry fire but stage 1 and 2 do. As always, safety is paramount. Double check your firearm is unloaded and you have a safe area. Read the stage and string directions and practice the draw, acquiring the sight picture and getting the shot off. The first stage has several strings that require one-handed shooting with either the strong hand or the weak and this is something that we don't practice very often.
The second thing to practice, and this is my problem, is to not worry about shooting fast. You want to shoot accurately. The second and third stage are especially important to have a good sight picture and hit accurately. It's real easy to miss completely at stage 3 and each miss is 5 points down or 2.5 seconds. Get over the urge to fire fast and concentrate on the sight picture and getting the shot off cleanly.
In my case I had two misses at stage 3 - that's 5 seconds added to my total time just for those two shots. A couple other shots in the 0 or -1 category and I would have made SS. The last time I mentioned I only missed SS by two seconds I also had a miss at stage 3 and those 2.5 seconds were the difference between Marksman and SharpShooter.
The other thing to consider about the classifier is that it's not the end of the world not making a higher classification - I'm just hung up on it for ego reasons. We should all be striving for accurate hits, not speed. The speed comes naturally with practice if you concentrate on getting hits first.
Ray