Don't spread your investment thin
The single biggest early mistake is levelling every hero a little. Upgrade resources are scarce at the start, and a roster of evenly mediocre heroes loses to a roster with three genuinely strong ones. Decide who you are building and pour resources into that short list. You can always broaden later; you cannot get wasted resources back.
Pick one troop type to specialise in
Look at the heroes you already own and notice which troop type — Cavalry, Archer or Footmen — you have the most ranked heroes in. Specialising in that type gets you to a competitive lineup far sooner than trying to build all three at once. If you are torn, cavalry is a common starting focus because of its aggression, but the right answer is simply the type where your roster is already deepest. (New to what the types mean? The troop type guide covers it.)
Let the generator tell you what's reachable
Instead of studying tier lists you cannot use yet, put your heroes into the combo generator. It will show you the ranked combos you can already field and the ones you are just short of. This turns an overwhelming game into a short, concrete to-do list: here is what you can play now, and here is what is nearly in reach.
Chase near-misses, not dream teams
It is natural to fixate on the #1 lineup in the game, but if it needs three heroes you do not have, it is a distraction. The fast route to improvement is your near-misses — the strong combos where you already own all but one hero. Completing one of those is often a single unlock away and immediately upgrades what you can field.
Upgrade the heroes your best combos share
As you look at your reachable combos, you will notice some heroes appear in several of them. Those shared heroes are where your resources work hardest: developing one hero who features in four of your lineups improves all four at once. The generator's "best heroes to unlock next" suggestions are built on exactly this idea — follow them and every investment opens up more of the rankings.
Revisit as you grow
Your roster changes constantly in the early game, and the best lineup for you changes with it. Come back to the generator whenever you unlock a hero and re-check your groups — a single new hero can quietly complete a combo that was out of reach yesterday. Keep an eye on the current meta too, so your plan follows the rankings as they move.
In short
Concentrate your investment, specialise in one troop type, build the combos you can actually reach, and prioritise the heroes your best lineups share. Do that and you will have a competitive first lineup while other new players are still spreading themselves thin. Start with the generator and see what your current heroes can already field.