This must be one of my favorite kinds of proofs. When you have a mathetical expression that contains an arbitrary integer of some sort, in most instances it is n, the expression holds true if the condition fits for all n + 1.
However, before even starting the induction step on your arbitrary integer, you must prove that the base case holds. This is so very important because it gives you a foundation to lay on. Without it, your proof has nothing. How are you to prove that n + 1 is true if you aren't sure n is true? I particularly like induction proofs because of these base cases, they are something so integral to nearly any algorithm that you find in computer science.