When practicing my forms what should I focus on most?
There are three things you should always focus on.
Basics Basics Basics
Look at your posture. Ensure you have the lowered your centre of gravity but have an upright carridge.
Look at the angles of delivery of your blocks or strikes and examine the methods of execution you are employing in your movement (Thrusting, Hammering, Whipping etc).
Look at the attack you are defending against and make sure your strikes are to the correct target in height and depth of action.
Remember a form allows you to express your full range of motion. Practicing with a partner means you have to hold back some of your force to prevent injury to your partner. In the forms you don't have to worry about this.
Within the higher forms it's up to the individual martial artist to decide what movements they wish to be major of minor strikes. This gives them a feel for their own style of movement and expresses their thoughts on the moves contained within the form.