When you have a weak, low-level deck like mine, you need to be selective when choosing opponents in the Deck Wars Tournament. Don't forget, my heroes are intentionally set at a low level (3 and under) so that it costs only 1 heart to play each match. So I fight only Finn and Jake. Why those two? Because other heroes are available only through playing quests or from the Algebraic chest. Either way, heroes that aren't Finn or Jake usually indicate a player who has worked on building his or her deck, and we want to avoid those kinds of players. In fact, is usually preferable to play against Finn instead of Jake, as Jake has a Floop to give +3 Attack to all Corn Field creatures.
Secondly, we want to look at the landscapes. Usually, this is the best landscape -- Corn Field, Corn Field, Corn Field, Useless Swamp (CCCU).
This is usually the best landscape because it is the default landscape, as the deck you initially start with has a bunch of Corn Field cards and some Useless Swamp cards. This deck is also good to fight against because it usually indicates the opponent hasn't added any Blue Plains cards yet, possibly because they haven't fought beyond Quests 3, 5, 6, which drop Heavenly Gazers. But there is no guarantee, because your opponent might have some fancy Useless Swamp cards, like Tree of Underneath.
In my experience, this is the next best landscape -- Corn Field, Corn Field, Useless Swamp, Blue Plains (CCUB).
This usually indicates an opponent who might have added some Heavenly Gazers or Cool Dogs to the deck, which are usually from earlier quests.
The next best landscape is kind of iffy -- Corn Field, Corn Field, Corn Field, Blue Plains (CCCB).
This indicates someone who has intentionally removed Useless Swamp cards and added Blue Plains cards. This indicates some planning, so possibly a more advanced player. You might see someone with Cool Dogs, Woadic Time Walkers, Ancient Scholars, and Axeys.
Watch out for this landscape -- Corn Field, Corn Field, Corn Field, Corn Field (CCCC).
This is the kind of deck that I use and indicates that someone who has done some planning and is trying to avoid forced empty lanes where you have a landscape but no card to place on it.
Also watch out for these.
Basically, anything that is Sandy Lands or Nice Lands, because that indicates someone who has played advanced Quest levels to get some chest drops. Nice Lands chest drops start at Quest 10 with Princess Bubblegum, and Sandy Lands chest drops start at Quest 13 with Flame Princess.
Here's a good place to find out which cards can be dropped in each Quest:
http://cardwars.wikia.com/wiki/Quests