Count Zero, the only intelligences that I have worked with have been angelic, and I would certainly highly recommend this path. While it may not be the most popular on here, it’s the path I’m most interested in at the present time.
That is not to say that there isn’t a ton of fantastic information from EA’s “Evoking Eternity” (as Soundwave specified), whether or not it’s more heavily aligned to a left-handed path-working.
The first spirit that I worked with was indeed the Archangel Raphael. The experience was amazing, full of warmth and a sort of fatherly love to it. He makes his presence known quickly during the conjuration and for me, he had a very ‘touchy-feely’ energy to him. For this reason, it is no surprise that he is an angel of healing and protection.
My advice would be to do research on the Archangels you wish to work with. Figure out their days of ruling, sigils/signatures, ritual candle colors, etc. You could try a handwritten letter to the Archangel, with a list of questions or whatever your desire may be, or just simply focus and redraw the sigil on a piece of paper, thinking about communicating with the intelligence - what does the sigil mean to you, paying attention to the smallest of details in line-weight, etc.
When you get into the actual ritual, it’s okay to vary from a specific written routine and to make the ritual your own. It’s most important to flow with it and listen to your body and mind - be attuned to the subtle vibrations and change of surroundings so that you can be aware of the spirit’s presence. Focus on your third eye visualizations and be open to what you are being shown, along with asking questions directly after a certain visualization.
I’m no expert, but it really is different for everyone, I think. You should just give it try, and have confidence in your abilities. Don’t expect to have a full-blown physical manifestation your first evocation, but certainly pay attention to the sensations and inner-dialogue going on.
Good luck, angelic entities are very rewarding to work with from my experience.