I learned to make omelets by watching the fine folks making them at This Ain't The Only Cafe in Sudbury, which is now the Laughing Buddha. Secrets I learned: 1) Adding water instead of milk to the egg mixture helps the egg stay together. 2) Fry your veggies in olive oil and douse liberally with good balsamic vinegar and spices.
Here's what's going into my 4 egg omelet: zucchini, shrooms, tomatoes and havarti cheese.
Frying everything up, I added fresh thyme and balsamic.
Eggs go into a medium hot, oiled pan. 
Once the eggs have somewhat solidified, add the cooked veg and top with cheese. Let it cook for a minute or two.
Now comes the fun/hard part. Flipping! Be brave and go for it. Hesitation is not your friend when flipping an omelet. But if it rips a bit, as you can see mine did, comfort yourself with the fact that it will still taste delicious with these slight imperfections. Makes life interesting, no?
Here's my half! I like to eat all omelets with sweet chili sauce.
