These are just general tips that are useful in my opinion. You might not agree with some of these and you are free to discuss about them and add in more tips :)

1. Always check enemy inventory and tell your team. Check their items from the moment they arrive in lane until you have won the game. In early stages, checking their regen supply is always good to keep in mind when harassing the enemy in lane. Later in the stages of the game, it's good to check if they have picked up core items or not. Such as blink dagger, forcestaff, bkb, and etc.

2. Carry a tp and use it efficiently. You don't always have to teleport back into lane. It's always debatable and situational whether you should tp into lane or not. As an offlaner, unless you are missing out on exp or last hits, you don't always need to tp back in. Also, by saving the tp, you are able to tp into another lane if needed. For supports,

3. As a support, when babysitting your carry, always try to go around the trees and get behind the enemy offlaner (if they are solo) and harrass. This is to not aggro the enemy creeps. You should try to make them use up their regen and try to get them way from experience range.

4. If you buy a quelling blade, use it. For example, if you are radiant and you get it at the beginning as a carry, cut the tree between small and medium camp for your support to pull. You can use it to create new paths when escaping or ganking and so on.

5. Use the night vision range to your advantage. It's really useful when you are ganking or using your ally as a bait. Because of reduced vision in night time, you can be behind your ally or creep that you are in range to help when they are ganked but still out of vision of the enemy.

6. Clear stacked neutral camps with your supports. When clearing camps, try to clear them with your support nearby, so they get a boost in levels. It'll make your supports much stronger for ganks and team fights.

7. As a support, be active. Always try to harass enemy in lane. Either stack and pull or double pull in order to deny enemy exp and farm for yourself. Check runes every 2 minutes. Right runes are really powerful for supports in the early stages of the game for supports to gank and secure kills. Smoke and rotate to other lanes to help out if you are unable to do anything in your current lane.

8. Ward smartly. There are a lot of good warding places other than the general rune and jungle ward spots. Before deciding on pushing with your team, you can put a ward behind the enemy tower to see who is coming in to defend. If your team is ahead and has an advantage, put some aggressive wards to give more map control for your team.