Bard is a really fun support that can apply a lot of map pressure. He isn't as strong in lower ELOs since people don't really communicate and cooperation is almost nonexistent. You won't be able to do much on your own, but if you bring along a good duo partner you'll have a good time.
Maxing [img=skills/bard/q.png] first is pretty much a given. It's Bard's only skill that does damage and you need to have this on the lowest CD possible. Upgrading [img=skills/bard/e.png] second gives you a shorter cooldown and makes allies move faster while using the tunnels. This can be really useful for baiting the enemy. I don't think [img=skills/bard/w.png] improves by much so I max it last.
In the early game you should make favorable trades with the enemy. Try to stun them against walls, minions, or each other. Usually a good stun will result in a won trade. You can use your shrines to keep your ADC healthy, but watch your mana. Magical Journey can be used to set up ganks with you jungler or to get away from ganks. You can also help out fights in the river very easily using your Magical Journey.
In the mid game you should try to collect chimes and maintain ward coverage. At this point you should have sightstone and a sweeper. Make sure you group with your team if they need you. I've gotten caught up getting chimes and missed teamfights before, It will usually result in angry teammates. Your ultimate is really useful for diving towers and securing objectives.
In the late game you should keep up ward coverage and map control. Getting picks at this stage of the game is really important and can win you games. Ulting a lone enemy can result in the pick that lets you take baron, an inhib, or win. Don't be worried if you whiff your ult, the CD is short. It's better to try and hit the ultimate and miss than to hold onto it all game. Yo can easily shut down enemy engages by ulting them if necessary.
In teamfights you should try to stay on the edge of the fight and CC key targets. Peeling for your ADC is also important, so don't forget about them. Using your ultimate is a pretty huge judgement call in teamfights. You should use it to keep people out of the fight or to save one of your squishies. If someone is in zhonya's they won't be affected by your ult. Just remember that the longer you're alive the more meeps and Bindings you get to throw out. Sometimes it's good to take risks to take out key targets, but try not to throw by overextending.
I'll try to update this guide as I play Bard more. He got buffed recently, so I haven't gotten enough games on him to have a final opinion. This guide is just my thoughts on how best to play him.