Using a flame is always best, burgers cooked over a grill always turn out better.
If that is not an option, use a lower heat setting and flip them about once a minute. Also if you have a more homogeneous burger mix (like not as big chunks of onion or whatever, everything is finely diced and mixed very well) then it generally results in a more thoroughly cooked burger. Additionally, in my opinion burgers are best when cooked medium rare, so it should still be pretty pink in the middle to taste all that natural juicy goodness.
Yum you made my hungry!
