How to become a reader
1. Get friendly with your spirit guides. Your spirit guides are sort of like your interface, your translators, for the information that you will receive from "the beyond". (Yes, I know it's Professor Trelawney cheeseball, but I can't think of any better description.)
2. Start asking them questions about stuff. Sometimes they'll talk to you, sometimes they'll show you situations sort of like in picture or movie-ish form, and sometimes they'll introduce you to other spirit guides that will either talk to you or show you stuff. At least, that's how it works for me. And when I say "talk" and "show", I don't know that I actually am seeing or hearing anything. For me, it's sort of like the information just shows up in my mind, kind of like what it's like when you are recalling a memory of a movie that you watched. It's different for everyone, I think. I get particular physical sensations when I have a strong connection.
3. Start writing down your impressions in your journal. If you're going to be walking between the worlds, dumping into a journal on a regular basis is necessary.
4. Practice describing what you see without value judgments. Basically, relate exactly what you see. Get your opinions out of it as much as possible. Some things that you see won't make sense. Don't try to make them make sense. If you see a huge banana in a sailboat, you see a huge banana in a sailboat.
5. Start practicing on other people. I like to have a little ritual when I start a reading for someone else wherein I ask for only my and my read-ee's highest and best guidance to be present, and to be a clear channel for the information that we're about to receive. Then, ask the questions and start relating the answers. It takes some practice to get used to coming in and out of meditative or semi-meditative states to ask questions and relate the answers, so starting on friends can be helpful. For me, it's actually easier to read for complete strangers, because I have a tendency to editorialize (add information that's not there and insert value judgments) when I'm reading for friends. Close the reading by giving thanks to the guides that were present.