These are my beliefs on guardian angels. i am not an expert i cannot hear mine but i feel my angels influences in intuitions and sometimes in little signs or "co-insidences." so here is what I think.
1. Guardian angels like almost everything on this plain and other plains, they are made up of energy. in the same way that you cannot see the wind but can feel it, is the same way to approach your guardian. Belief is the key to building up a link with your guardian. you cant see the wind yet you know instinctively that it exists.
2. Build up a connection by inviting your guardian to visit you in your dreams and see what happens.
3. Ask. Again our subconscious is more receptive when sleeping or dreaming so just before you drop off ask your angel to try and communicate their name to you.
4. Our guardians are always in reach. The more you communicate the more you will feel their everyday presence. Its thier job to help you to develop spiritually and prepare you for the next step.
5. Like you talk to anybody else. I talk out loud to mine – usually when no-one is about so i am not guarded in what i say. but you can talk to them in your head too.
6. I believe animals have their own guardians like nature spirits, some Fae. I also believe that our guardians can influence animals if we need their help. ie. dogs who save people from fires/ avalanches, dolphins who save people from sharks.
7. yes. again prayer is just a way to talk to God, the one power, the creator whatever you believe Heaven to be and i believe it is possible to contact arch angels by calling them by name and asking them for help or guidance. iIn fact i once did this in an emergency situation while searching with police for a woman who was determined to die. We found her alive and she said that she had suddenly felt at peace and no longer wanted to pursue death. My plea for help had been heard on that occasion.
8. talk to your guardian as if you would talk to a friend. if you need help, explain the problem and ask them to guide you to the right solution. watch out for little signs from them. once when i was in my early teens i went to a dance without my parents permission. i missed the last bus home and tried to walk some very dangerous roads. i got very scared and asked for help. at that moment a car drove up and a very kind lady gave out to me for walking in such a dangerous place so late at night. She had a daughter my age and would never forgive herself if she did not make sure i got home safely. i got home safely. I would never get into a car with a stranger but I had a very strong intuition that my guardian was responsible for that pick up. If you dont ask for help they cannot give it to you. 
The more you talk to your guardian the more your communication will improve. you may never hear their "Voice" but you will feel their answer as if a thought just popped in your head. i hope the above has helped you connect.
all the best
D