Probabably the best thing anyone can do to start with is to lower the weight.
Trying to beat a personal best from the start is the worst way to learn mind/muscle connection. You'll be using every muscle, sinew, joint, bone, the lot, to push the weight.

Next best is to slow the rep. For example, flinging up a dumbbell when curling that is too heavy will engage legs, back, shoulders, calves and toes as well as biceps. Lowering the weight and slowing the rep and making sure the only muscle contracting is the bicep will engage the exact muscle you intend building. Some say it helps to visualise the muscle doing the work.

Once you get it right there's no turning back.