Any advice re sending out a demo-reel (abstract work & graphic idents at this point)

Hi. I’ve worked up my first demo-reel of abstract work, and am currently working on a demo-reel of graphic idents etc. I’ve received and acted on critique on the abstract demo-reel, and have been encouraged to start sending out the reel to prospective clients. So, I wonder whether anyone can offer any advice on : how to decide on which companies to approach; the best way to submit the reel, technically; how best to word any covering email / letter accompanying the reel; etc.

I don’t think I need any further pointers on creating the reel itself (as I’ve researched that quite a lot already, and have taken that on board in creating the reel). I’m just concerned with how best to start making approaches to companies, with a view to picking up some work.

Any guidance greatly appreciated. Thanks!