redbug has some very good points there.
Just like real life, there are going to be (to put it nicely) rude people. I have seen these rude ones that basically keep the co-angler away from the areas most likely to carry fish, and in those cases you just make the best out of what you can. I tend to be a pessimist when it comes to certain situations and my experience around some smaller local tournaments has helped me keep a pessimistic view on them. Official and larger tournaments that have anglers used to running with a CO tend to be less likely to have a meanie, since they are there and know the rules, and used to it. All the same, don't be rude yourself. The bass trail has anglers that talk to each other and you may burn your own bridges with the anglers willing to take you out with them.
Typically it is best to bring 1 or 2 Planos, or reasonable sized tackle box and keep it close by and out of their way. Usually the rod limit is in the 4-6 range. Don't forget to offer gas money, depending on the stakes and entry fees, usually $20-40 (depending on the size of the lake) is a good range, AND MAKE SURE YOU HAVE THE CASH ON HAND. If the person does more boating than fishing then that is their problem wasting the gas, not yours, so don't feel bad about refusing to give more gas money in those situations. If they sit in one spot most of the day, then less gas money should be an option.
Also make sure you go over some ground rules with the owner (including gas money, set the amount to start with) as some people prefer to do things a certain way. Don't feel bad about reporting the overly rude or overbearing boaters to the tournament staff, if they get enough complaints they may just bar that person from their tournaments that require co-anglers. I have been to (but not fished) several tournaments over the years where a certain group sees co-anglers as a burden and cause all sorts of problems, or purposely keep the boat in positions that gives them (what they think is) the best shot at fish. Assess the situation and use their rudeness against them, many times you have the opportunity to outfish them by going a different direction that suits the back of the boat. Of course if you start catching in those cases, I have seen where they swing the boat around taking your productive spot on purpose. Thats when you change up your technique and continue to use your area of the boat to continue to catch fish.
Many times you will get a great owner and they can become a friend, just do not push your luck with even the friendliest of owners. Bring what you expect to need and use (including your meal(s) :mrgreen: ). If you don't have something, then just find another way with the gear you have, do not expect the owner to freely lend any lures or gear you may not have.
If something major breaks, ask them if they want help, don't automatically jump in trying to take over thinking you know how to fix it unless you are a certified boat mechanic and really do know (if thats the case let them know in the pre-launch discussions).