When building new deck u should follow simple rules:
1. Decide how new deck should win, killing, building or resource. First 2 are easiest to craft. Dont build deck trying to win both ways. U cant compete vs good crafted decks that way.
2. Then adding card to new deck u need to be sure that u gonna play and can play most of cases that card. Otherwise u can easily end up hand where u have only situational value and have no option just to discard. Discarding card is worst cenario.
3. Resourse usage. U need to balance deck that basic and common cards use all resourses. If you focusing attacking always look cards what can raise your recruits stock at expence of some other resource.
4. Keywords. If u use keyword deck u need almost pick every that common keyword card. Otherwise keywords wont be effective since u cant fill your hand with that keyword fast enough. Rest commons should be resource and few 1-2 defence cards. Example Undead is most dependent on keyword. So u should have 4-5 nonundead commons max in deck. Otherwise u waste way 2 many turns to get our anything from your keyword.
5. Synenergy. There is so many cards what synenergy very well in game. Example
a)Siege preparations->Oasis->common restaration can give u so big starting stock boost that u can now play few big cost cards.
b)Temple guard, northen mountains, supply units synergy very well
c) Rejuvenation can offer very many powerful combos.
6) Every good deck should have, hand discarding cards. Since there are many card what fuck up your hand and spending 3 turns jsut to discard those cards can cost you a game.
7) Card cost effecviness