You must make the moves which address your position. If you have an IQP let's say and you start trading minor pieces with no plan in mind, this is a mistake. Even if a computer might evaluate your moves as good.
It's important to have a plan. Even a bad plan is better than no plan. Your plan doesn't have to involve complex Rube Goldberg-like maneuvers, it could be as simple as "my opponent has a backward d pawn, so create an outpost for my knight on d5" and make moves that help you accomplish that task.
Identify some weaknesses in the opponents position - weak square(s), overloaded pieces, isolated or backward pawns etc., and come up with a plan that exploits the weaknesses. If you have a passed pawn, come up with a plan for controlling the squares in front of it so you can push towards the 8th rank.
Start small, with plans that will only take a few moves to accomplish. The more games you play, the easier it will become to create more elaborate plans.
Of course your opponent will be making moves, too, and might make a mistake - so you have to be flexible and aware and possibly change your plans accordingly.
Originally posted by National Master Dale Trying to avoid mistakes I suspect would cause one to play bad moves in a useless kinda way.Perhaps h3 or a3 to often instead of activating your whole army maybe.
One might lack direction or purpose to ones moves if they were why not instead of why kinda moves.
Making a passive move such as a3 or h3 instead of developing is a mistake. At the very least it wastes a tempo.