Proper form is the number one most important aspect of exercising. Nothing else matters if you are not in good form. (Remember this if nothing else below grabs you!)
So you are thinking about trying out a new workout program or getting started? The best advice I can give is to seek out a trainer and many gyms will give free consultations/personal training sessions for new clients. It is completely worth is to spend the money on a session to learn the basics; squats, lunges, push-ups, planks, abdominal curls, flat back exercises. Once you know where you should be in stationary exercises you can begin to progress into more challenging, complex and dynamic exercises.
Start out with light weights to perfect your form and then increase. You should feel the work of a bicep curl mainly in your bicep, if you start to feel it anywhere else more so than your biceps a few things need to be adjusted; form and/or weight. There is no shame in decreasing weight, especially in a class setting.
With good form you will avoid injury!
Give yourself adequate time to recover in between intense workouts. Your muscles need recovery in order to become stronger, if you continue to work out on sore muscles you will continue to breakdown muscles rather than build.
You do not need to be sore to have had a good workout. I hear this all the time, "It was good, but I wasn't sore." Try thinking about your post workout feelings like this; I am not sore, wow! I must be in really good shape to have made it through an intense and/or challenging workout and feel this great the next day.
I would love to hear your exercise questions and thoughts! Have a fantastic day!