What champions do you already play? That'll help me give you some supports that fit your playstyle.
As to "being a bad support," I would give you pointers, but what you should do in a given situation can be very different depending on who you're playing, who you're playing with, and who you're playing against.
In general, though, you should have three over-arching goals:
- Keep your adc safe so they can farm (including: protection from harass and engagements in lane, and ganks).
- Try to prevent the enemy adc from getting farm.
- Have very good map awareness (watching for ganks, pinging when you see the enemy jungler, etc).
Generally, the more aggressive you are as a support, the better you can accomplish goals 1-2. The tradeoff is that being more aggressive also puts you at risk of getting harassed or engaged on, to the point where you can't accomplish those goals anymore for fear of dying.
Note that getting kills, for you or your adc, is not on this list. That's because kills are opportunistic and happen because of your enemy's mistakes. For example, say you harass the enemy adc until they're at 1/4 hp. They now have a choice. They can play really safe, and miss a lot of farm, or they can be less safe, and try to get the farm. If they don't play safe, they just made a mistake, which you can capitalize on and get the kill. But you can't get the kill unless they make the mistake.
Again, that's not to say you shouldn't harass, or look for kills when the opportunity arises. You should just be aware that kills happen when you capitalize on their mistakes, not because you decided, "I'm going to get a kill now!"