I finally sold a TV script and I get to go on my first shoot in a few weeks. What are the best ways for CWs to help on set?

Your first time? Observe. Follow your producer’s lead, and communicate through them to the set. If you’re asked your opinion, be clear and direct because you’re burning money and daylight. Never eat before the crew and be sure to thank them when you wrap. Don’t try to help them with anything, either; they’re union and it will look like they can’t do their job so they won’t be asked back. Take in the entire process and you’ll be 10x better writing scripts from now on because you’ll understand how they’ll go from paper to final produced work.

All the above.

Plus, I like to have a page of alt lines on hand in case something isn’t working. It’s rare you get asked for them, but it really helps on the off chance you do.

Also, I would take notes on little differences in takes on set. It can be super helpful in the edit.

So... you’re not senior

Yes to what they said, and I'd double-down on alt-lines. I've shot 30+ spots and had alt-lines every single time. You never know what will work and what won't until you see it happening, and you should have a bunch of alts, including some of your best, most desired lines to slip in a take if possible. Some directors love it if you have kick-ass ideas for alts, others not so much, but it never hurts to let them know you have some lines and if they like them, they'll find a way to work it in. I've had numerous scripts get better this way; on-set, just spit-balling lines with the Director and talent, too. Remember, this is YOUR script. Respect your elders, but stand up for your art and if you see something don't be intimidated into silence unless everyone is screaming or crying. That you should sit out.

Pay attention to things actors do and say during callbacks. You may like something and then use it when shooting.

All great advice so far. I’d also add that you’re there to work and not just take it in. Be sure you’re grabbing the options you need to bring your original vision to life. Producers will want to move on from shots the entire time. Be confident you have what you need before you go though. Doing this will make your edit much easier.

think of the story you’re trying to tell. you are the voice of the story on set. your AD may be wrapped up in the minutiae of the visuals looking pretty (and you may be too), but you’re looking out for how it all adds up to the narrative. however simple or complex that narrative is.

I think it’s also worth noting that the production will happen with or without you. Make sure your (the agreed upon) vision is being executed. Don’t be afraid to ask questions. If it’s dialogue heavy and you’re squeezing a lot in use a timer to make sure it’s roughly within time limits

Ooo this will be fun...Anyone have any first-time-on-set horror stories?? For me it was my art director partner completely and totally shutting down from the pressure, rendering them speechless. I learned to always have an opinion ready on that shoot...

Agree with all of the above and will add that you should always time out how long each line SHOULD take to deliver. Time the actor on set. Most times, they deliver lines too slowly and that will bite you in the arse in edit. That said, write SHORTER alts as well as longer ones.

Same goes for the rest of the scenes. Know going in how quickly you need to capture each action. If there’s a particular thing you need the actor to nail, make sure they rehearse beforehand.

If there is a script supervisor on set, make friends with him/her. They help a lot! Chat before each setup to make sure you guys are on the same page.

In addition to ALTS, think about what you could capture and repurpose for social. Stills and video. Do you need to capture anything vertically? Shoot wider, you can usually punch in. Ask the producer what camera they’ll be shooting on and how much wiggle room you have with that.

If there will be any supers onscreen, leave room for those too.

Also, let the actors warm up and let the director do his/her thing before making comments. Be respectful of the process and let them work, but don’t be afraid to speak up if they’re not getting what you want. In the end, remember that they will all walk away from this project after the production but you will see it through til the end!

Good luck!

Visualize the whole thing beforehand, but be flexible. My first shoot as a Junior Copywriter was super-low-budget, shot by the CD's "Director" buddy, and in the very first scene the Director couldn't figure out how to get the action moving to get from the first scene to the next, and so I had to step in and choreograph the talent and direct the director to get the shot.

1) The crew eats first.
2) have alt lines - be prepared. If something doesn’t sound right or isn’t delivered right, start writing
3) stay off your phone.
4) don’t be afraid for someone else to write or come up with something. My first time i wanted full Creative control and was worried It “wouldn’t be mine” if someone else came up with It. The voice actor (radio) came up with a really funny alt., and on another script the brand manager came up with something.