Don't be in a hurry to buy anything on your first walk around go around and check each table one at a time and make notes or keep in mind what you see that interests you and note what and where it is.
Many things are way overpriced so expect to haggle or negotiate on price many people pay too much by buying at the sticker price.
I would check with online auction sites such as gunsamerica gunbroker and auction arms noting fair market prices write them on a small piral note pad for anything I would be looking to buy.
Pick up or order a Gun Blue Book Price Guide and highlight or mark any pages that are of interest.
Many good deals walk the floor or walk in the door so if you go very early and walk the floor once or twice it often pays to hang around the entrance as much as possible and be among the first to see what someone walks in trying to sell.
If someone walks in with something of interest at least try to get a phone number many potential sellers get disgusted with some of the lowball offers gun show table holders give them and end up selling it for less than they originally had it marked.
Bring a small mini flashlight or buy a bore light or at least have a business card and light with you so you can use it to check the bore and chamber.
check whatever you are interested in out from one end to the other but do so without showing any emotion or attachment be prepared to walk away when haggling you can always come back and haggle some more but your money only goes once.
Bring LOTS of cash most people prefer it.
Wear comfortable shoes and bring snacks as the food is usually overpriced as well.
Many good deals are offered on the last day a few hours before closing time so if something talks to you and it is not rare or a gun in high demand it can pay to go back the second day.
Good luck and good hunting.
You might find something you never thought to find, and come home with it. 
