as a former support main, here are my two cents for you.
1, show your support some appreciation for their vision. tell them thank you for the vision when they place wards out. ALWAYS upgrade your trinket at level 9, whichever trinket you have. USE the trinket. it should be constantly on CD, trust me your support will notice you trying to help them out and will make note.
2 tell them thank you. encourage them when something bad happened and when a good play is made give them credit for setting it up. there have been times I pulled a penta because my support locked them down. without the setup I would have died 2v5 but my support did well and people tried to give me the credit.
3 don't encourage them to build damage. if they want to they will and if they want to build support then its cuz they wanna set you up. Encourage them to get money where they can, assists are a big portion of that. One tricky thing to helping out your support is that if you are in a fight and see your support coming, try to stall an extra second so they can get the heal/shield on you so that they get some assist gold. I know the frustration of wanting an assist and the zed pulls a penta when he was a mere 50 units outside your heal range.
4 post game gifting is above and beyond. If you have the cash its amazing to do, but no one expects it and you should reserve your money for yourself.
5 most importantly, ask your supports that did well to play with you so that you can learn how to help them out better.