There are a couple of income sources:
- default gold you get each round;
- 1 gold for winning a round;
- up to 3 gold for a winning or losing streak;
- 10% interest from residual gold (capped at 5 gold)
The best way to earn gold, on theory, would be to be on a very long win streak while also saving up gold for interest. This, of course, is hard to do.
The worst scenario isn’t to lose a lot – it is to alternate between winning and losing each round.
In that sense, if you are struggling, going on a losing streak could be done on purpose so that you will be able to recover economically and win in the later rounds. This is more costly to do the later the game goes because opponents have more units and you would lose more HP. This strategy is called “selling your blood”.
Interest: In the early game interest is insignificant, but in the mid-late game, you might want to consider saving up some gold to increase your overall income. It is a common strat to try to get to 50 gold after you are lvl6-7 (in the mid game), in order to prepare economically for the late game.
Selling: lvl1 units are sold for full price, so buy pieces that you want to upgrade later on even if you are not using them to fight. You can always sell them off if they become useless because you change your strategy. You have 8 reserve slots to store units you don’t currently use in battle. Usually, you want to keep units there that would help you upgrade your current fighting heroes.