If it's clumped up as you drain it make sure you use plenty of salt (make it as salty as the Mediterranean Sea!) and that it has lots of room to boil in. Also be sure to give it several stirs as it cooks, though it's especially important when you first submerge into the boiling water.
It may be over-cooking that causes the clumpy pasta. Angel hair takes only a very short amount of time to cook. Cook it until it's just a tad bit under done (the infamous al dente "to the tooth", which means it's not a squishy mush but has a little bit of solidness [not crunch] in the center of the pasta as you sink your teeth into it). Pasta will continue to cook from the trapped steam and water if you don't drain it well which can just compound the clumping problem.
The other trick that was already mentioned is to sauce it immediately.
The only time you you should need to add a tiny dash of oil after its drained to prevent sticking is if you're not going to use it right away.