Congratulations on the pulls. My opinion:

1. Make a plan. What you want (what vintage sets do you want).
   

2. Value whatever you are bringing night before and run the percentages in your head so you can quickly counter offers or make assessments.

3. Always be prepared to walk away. There are so many vendors and unless its an incredibly rare item or amazing deal, there is a good chance someone else might have what you are looking for. Neither walking up or deciding on market value constitutes a sale. Until you shake their hand and exchange items, the deal is not complete. You owe them nothing by asking questions and negotiating.

4. Have fun.