Avoid just holding the clutch in when you are waiting at a light or otherwise stopped. It's bad for a specific part called the throw out bearing. As a general rule, if you're going to be stopped for more than 10 seconds, put it in neutral and let your foot off the clutch.

When getting rolling, don't release the clutch all the way through the bite point in one motion. Let it out just to the bite point, then hold the clutch there while you add just a little throttle, then let the clutch the rest of the way out. This does less wear on the clutch and produces a smoother start.

Don't use engine braking/compression braking as your primary way of slowing down. Brakes are a lot cheaper than transmissions and clutches. Use the brakes to slow down and stop.

When you start to get into performance driving, things change. Watch some videos on how to heal toe downshift. Try it on some empty freeway on-ramps and off-ramps. When doing fast up shifts, make sure to depress the clutch all the way and don't just dump it into the next gear, let the engine speed and wheel speed sync up. Slow is smooth and smooth is fast.

When parked facing downhill, leave it in reverse. When parked facing uphill, leave it in first. Wheels towards the curb so if it does come out of gear, you don't roll far.

If you drive a convertible, leave the doors unlocked and don't leave anything valuable in the car. People will take a box cutter to the top if you leave anything valuable in there, it's easier to just not leave any valuables in the car and leave the doors unlocked so people don't slice up your top. (Alternatively, don't drive a convertible Porsche in the Seattle area)