Enochian angels are very different from other angels. They reside in a different relam to other angels and to evoke them requires certain criteria, such as the tables and squares, and conjurations in the Enochian language, that are not required for others, such as the more well known archangels.
If you want to start working with the Enochian angels while you gather the materials to evoke them, I recommend travelling the Aeythers. The book, The Lost Art of Enochian Magick by John DeSalvo, provides great meditations for this, and it also comes with a CD of the Enochian Calls for proper pronunciation.
Non Enochian angels can be evoked in a far easier manner. I, personally, use the same basic set up that I use for demons.
Damon Brand, of The Gallery of Magick, provides some original seals for calling upon angels in his books, though they are not Enochian angels.
While some people use invocation and evocation interchangeably, traditionally, invocation is calling the essence and power of a spirit within yourself, and evocation is the summoning of a spirit into physical manifestation externally to yourself.
Contrary to what @The_Wizard_Rudra said above, invocation is NOT possession, as the consciousness and personality of the spirit do not become a part of you. When you invoke, you are only calling upon aspects of the spirit, such as invoking the power of Mars for courage in conflict, for example. Unlike possession, the spirit’s voice is not in your head when you invoke. You are simply taking their power within yourself.
As far as I can tell, angels don’t really do the possession thing. That’s not to say they can’t, but more like they decline to do so. In my experience, they don’t have the desire to experience the physical in the same way the demonic do, and so possession doesn’t interest them.