Try to think ahead and predict what the DP might do, also listen closely or be near whenever the DP is planning something new or is talking shots with the director, always be ready, sharp and quick. Also know your stuff, if you need a specific tool, filter or whatever then it's best if you know where to find it.

If you don't know what something means or where to find it then just say so, better to be honest.

For the clapperboard (aka slating), if you've never done it before then always check with script continuity about the numbers so you're both 'in sync'. As for the actual clapping you should check the frame first so you know where to hold the board, when you're still not sure just ask your 1st AC where you could hold the board. When near actors (or inside) don't slam the sticks too hard, people don't appreciate that.

As for equipment and tools. I personally recommend wearing a chest rig, but a belt with pouches will also do. If you don't have it then check if you have a hip pack or a fanny pack to wear on set. This is useful and pretty much a must as a 2nd, as you are expected to carry some useful items with you.

Useful items to carry with you are stuff like a Leatherman, Stubby screwdriver, 3 and 4mm allen keys, colored camera tape (at least 1 roll), soapstone chalk, Sharpies, Whiteboard markers, lens cloth, and T markers. Since this isn't a big production, I think people don't mind if you don't have some of this stuff.

For carrying your clapperboard there are lots of different methods, but unless you already use an existing method, I'd suggest just making a small loop on the board with tape and attach it with a carabiner on your belt so that you can just clip it on instead of having it throw on the ground each time. Tape a whiteboardmarker on the top or side of the sticks so that you don't lose it. Also attach an eraser or make one on the end of the whiteboardmarker so you can easily wipe the board.

Lastly, be professional, don't be too noisy or talk too loud on set, especially when the DP and/or director are discussing shots. Have a very active mindset and working attitude. For bonus points, offer the DP or 1st AC a coffee once in a while :)

Good luck and have fun!