One thing to keep in mind its not just the lists you need to worry about. As you progress into the second and hopefully final round you will be playing more and more experienced players. They will not only know the rules for 40k and their army, but they will most likely know you army bakcwards and forwards as well. My biggest piece of advice I can give you is know you army, know the rules and read up on the top armies codex's. Knowledge is your best friend.
Here are some armies and what chance you might run into them:
Nob Bikers (Slim Chance)- Even though I have the army, this is a very easy army to play and it doesnt take much thought. You will see this in one of two ways, either all bikers in 2-4 units. Or you will see 2 biker units and the rest of the points put into boyz and deff rolla battle wagons. The scenario is a huge factor with this army, as in either case it will excel in kill points, and the horde version will do okay with objectives. Best bet with this army is use your transports to clog the board and block objectives off from the bikers. If you play kill points, reserve most of your army and nickel and dime him and hope you can get some good melta shots on his bikes. If he is on with his saves, this army will rape face, so hope he rolls shitty.
Imperial Guard Leaf Blower (Very Good Chance)- If you really want to know about this army, go to Bell of Lost Souls and search leaf blower. You will be able to read the article for the guy who one the last ard boyz with that list. If played by an experieced 40k player, you will be hard pressed to win. This list has an answer to everything in the shooting phase. Like any other guard army it will struggle in combat, but the trick is to get there. You will see a lot of templates being droped and a fair amount of flamers and tanks. the list normal has 2-3 Valks and they will be transporting the melta gun verterans and special weapon squads. If you dont win first turn you NEED to deploy in reserve. This may seem silly as you want to get across the table, but if you deploy your army, you will be wiped off in 2-3 turns and the game will be over in about 30 mins. get your meltas across the table quick and start popping tanks. This will be a tough match up, and since Adepticon had about 70% of the team tournament as Guard, you will be seeing this army almost for sure.