a) Ward. When in lane, ward the river and tribush. Ward anywhere ganks can come from. Always have 3 + 1 ward at all times. When in defense mode, ward our jg to prevent ganks. When on the offensive, ward their jg so that you can catch them off guard. The moment a team fight is about to break out, ward the surrounding area so that you can see their assassins ready to pounce on your carries, and ward right at the fight so that your top lane can tp into the fight. When baroning, ward so that you can see the enemy coming a mile away and are not caught off guard....similarly with dragon. Oh and always tell your team to upgrade their trinkets. Remind them it costs only 250 gold. Let them know that its not a BF that requires lots of saving up to achieve. If even one or two more people can upgrade, it will help your team have much better vision
b) At low elo, i have noticed that an aggressive sp is better than a defensive sp. Bot lane laning phase is determined by the supports, not the adc. Poke, push, deny, that's all your job. Experiment with aggressive supports, and try to poke their carries rather than their sp (did you know, the second highest diamond sp win rate in NA right now is brand.....he can easy zone and harass the enemy adc)
c) when you are with your adc and you are trying to push, always keep one ward with you at all times, so that if you push too deep in, you can ward the surroundings to catch mia enemies from pouncing on your adc
d) Call mias. Very important...not necessary but it helps a LOT and prevents your team mates from raging, which as we know can quickly escalate into their gameplay going whack very fast. If you don't see the enemy blitz sp mia in lane, call it. If laning phase is over, yet you still can't locate the enemy adc/sp and your mid is over extending....call it. Similarly, keep checking the mini map every 10 secs. If you see the enemy jg or top lane moving about to gank mid, send warning pings. Anything and everything you can do to help will be grateful. Similarly keep pinging and letting your team know about going after objectives. Tell them that you should NOT be relaxing when your team is leading in tower takedowns and enemy kills...and that you should continue to push your objectives. Ping towers that can be taken down. If your team aces the enemy team, and its easy to take down their tower, LET THEM KNOW, PING, AND INFORM THEM THAT THE TOWER SHOULD BE TAKEN DOWN if its a better preference to taking down baron. What good is a baron if after you get it, you are once again on the backfoot and can't do anything with it (this is situational , sometimes getting a baron can help with deep pushes or finishing the game)?
e) Damage equipment vs Utility equipment. Generally utility equipment including cc generating equipment is generally preferred unless your team composition specifically requires you to have full damage. If you see the enemy having a yasuo or yi, and your top lane is mana less and is building half tank/bruiser, get a frozen heart. Don't think that it doesn't go well with your kit....you NEED it. Get crucible so that you can have one extra protection for your adc
f) Aoe/cc in team fights. Your job is to protect your adc/carry. Unless you are a champ whose major cc/aoe is required to initiate team fights, save it for when the enemy pounces on your adc. Do everything you can in team fights to save your adc, including sacrificing yourself sometimes if required.
g) Save yourself where possible. If your adc is stupidly entering the enemy jungle, and their entire team is MIA and you have a hunch they are all there...warn your adc back, but dont necessarily stroll in with him unless you are confident you can save him from all the mia enemies. Whether it be in laning phase or post laning phase, if you dying isn't really going to accomplish anything, don't die. If your adc is about to get caught, and there is no way you going back to save his ass is going to result in in him getting away, don't go in and give them two free kills
I think that covers the majority of what you should do..... :P