If you play on Xbox feel free to join The Unforgiven V*
We complete the blue statue every week (almost 400 gems to get your collection kick-started!), and we can help you build teams.
Only requirement is playing — seals and trophies prove you’re active, and all your gold is yours to level your kingdoms.
Sales pitch over — that said, I agree pretty much with beeflog.
Other notable things to mention are:
Good teams often have scaling damage. Damage that scales can be increased fast enough and in large enough quantities to matter, so look at troops that have purple numbers on their card — these boost with magic. Also look at cards that can take all armor in a single cast, increase stats by a sizable margin (generally by being proportional to something else makes for better increasers, like shield of urskaya giving you armor that equals all opponents’ attack), or double a stat — these are almost always keepers.
Good teams get mana quickly so they can accomplish their objectives quickly.
On a good team there will be two or three distinct “jobs” cards perform, generally, and you probably want at least one of each on most good teams: generate mana, deal damage, support (usually by giving yourself positive status effects, or shutting down your enemy with negative ones).
Good luck either way, and have fun