Good luck. I know you’ve entered conformation so you have a sense of entering the ring to compete which should help.
No food or toys or lures in the ring or near the entrance. No treat bags or anything that looks like it could carry treats. No phone, wallet or purse on you as you enter the ring. Leave everything where you crate.
Do bring your own crate and chair so you and your dog will feel comfortable. Arrive about an hour ahead so you have to to potty your dog and have him get used to the environment of the rally trial. If your crate is in another area for conformation then you might want a friend nearby to hold your dog for the walk through.
Keep your leash pretty loose, not so loose that you trip over it, but loose enough that if your dog isn’t in perfect heel position he isn’t pulling on the leash. The rest of the leash will be folded up and held in your hand. No one will measure your leash so don’t worry. (I competed AKC Novice Rally with a 4’ leash. Beginner Novice and Novice Obedience requires a 6’ leash.) You lose points when your dog is out of position
AND you lose points if the leash is tight. Every time the judge sees a tight leash you could lose 1-2 points. Every time the judge sees your dog out of position you could lose 1-2 points so you can see if your dog lags at a 180° turn to the right you could lose 1-2 points but if the leash is also tight, now you are losing even more points.
Do read the rules, it’s very helpful to understand how they judge rally.
https://cdn.akc.org/Rally/AKC1086_ROR001_Yellow_Insert.pdf
You can talk to your dog to keep that connection but you can’t touch him in the ring. If the leash gets tangled under his legs (this happened to me when my dog laid down, ask the judge if you can touch your dog to fix the leash don’t assume you can lift a leg to get the leash untangled).
From the moment you enter the ring, until you leave, keep your focus on your dog. I never look at the judge when I bring my dog into the ring, I answer all questions to the judge with my head bent to look at my dog. This would be rude behavior outside the world of dog competition but expected in a trial. The time to look at the judge is during the walk through and after during the ribbons ceremony.
Take your full time allotted to walk the course in the walk through. Walk it as if you have a dog, hand signals, turning etc. everyone does, I call it our rally dance. I usually get three times to repeat the walk. This is your time to ask any questions of the judge, especially if you aren’t sure about a sign or it’s placement. Usually the sign is to your right, but there are some signs such as 20. Moving Side Step Right where you perform in front of the sign. This is when your dog will be crated or held by someone else as no dogs will be allowed in the ring for walk through. Bring the rally rule book or a rally app to the trial in case you want to look up a sign. You should get a rally map before the walk through to review and familiarize yourself with.
I count the rally signs in my head as I do them so I don’t miss one. I know a rally judge who reads the sign out loud. So she’ll begin at the start sign and she says to her dog “Number 1 is a sit” then when they get there she tells her dog to sit, the. She reads “number 2 is ....”. This is one way to be certain you don’t miss a sign.
Have fun and good luck in both rally and conformation.