It's really just as described Ronni. Fly the flag for your player if he's being given a hard time. Post about the good things he does. The idea of the Player Presidency is to support the player in any way you like. There really aren't any rules or time restraints. Some get right into it, others don't bother much.
Some things I've done for my players over the years are to arrange q&a's with PREnders, provide a bit of inside info where appropriate, correct inaccurate comments, report on form, injury, mention birthday, post newspaper articles about them, send a card and comments from PREnders if they have a bad injury, keep track of them at Coburg (if applicable). I've probably thrown in an odd poem or two, mentioned off-field stuff like charity work, visits to hospitals, time trial results etc etc etc.
Some start a Presidency thread on their player and update it throughout the year. It's probably a good idea if we all do that this year so there is a thread devoted to each player.
It's also a good idea to acknowledge your player in your signature so people know who the presidents and vps are if they want to contact you with some info.