I'm not sure I qualify as experienced, since my spinning addition is less than one year old, but that also means it's all fresh in my mind, I guess. I should mention that ive previewed CM, but have not been able to do it, so I can't give CM specific advice.
Cathe's already mentioned to expect saddle soreness, but it bears repeating. It will go away after 3 or so rides.
The biggest tip is to set up your bike properly, and Cathe addresses that in the intro to CM. Keeps the injuries at bay and makes it more comfortable.
The next biggest thing is to develop your pedal stroke so that you're both pushing and pulling the pedal, whether you're clipped in or using the cages. Before you can really do that, though, you have to build your endurance and ability to peddle with tension, so don't worry about it too much the first month or so...it WILL start to happen, but don't make yourself inputs over it... first you just have to be able to get through the workout. I loved it when I first started to spin, because I couldn't believe how hard it was...I can't tell you how long it's been since I felt like I exerted myself so little for such a huge cardio effect...not sure that sounds right, but I was getting a HiiT or tabata like cardio effect from just peddling...it was very thrilling and humbling at the same time. It was like going back In time and reliving how challenging I used to find even the easiest workouts and how much I had to modify...it gave me great perspective on everything I've gained.
But I digress...after you stop feeling like you're going to die and can make it through a workout pretty well, you'll find that there's room for extra thought...this is when you can really start working on your stroke. It won't come all at once, but each time you think of it in a workout, just think "push, pull" or whatever works for you, and actually pull up with one leg while the other is pushing down....and try to maintain that during the entire circle fo the stroke....i found it helped just to focus on doing this with one leg...don't know if that's advised, but it worked for me. it will feel weird to use this stroke at first, but most people adapt to it pretty quickly. A friend who's a cyclist told me that Greg Lemond (a true cycling God) said that at the bottom of your stroke you should move your foot as though you're scraping mud off the bottom of your shoe...I think that had to do with foot position, but it helped me to smooth out my stroke because to scrape off that mud, I couldn't do the stomping I was doing when I was just pushing and not pulling...it became very obvious because if I wasn't pulling up with my other leg as I was scraping the mud off my one foot, my stroke would slow dramatically or become a bit jerky. not sure if this is making sense to you as you read it, but get on your bike, add some tension and you'll see what I mean.
It's also important to pay attention to your upper body, which should be relaxed...you shoulders shouldn't be around your ears, your hands shouldn't be clenching the handlebars, Your back shouldn't be hunched, etc. again, all refinements to work on as you build your endurance.
Well, I cant think of anything else other than to have a towel and water bottle handy.
Happy spinning!
Trixoo