Important things to remember when using a heat press:

Always preheat the lower platen.
To do this, simply lower the upper platen onto the lower platen for approximately 30 seconds. This is especially important when applying your first graphic of the day. You don't need to do this if you are in the middle of long production run, since the platen will naturally be hot from continued use. Preheating the bottom platen helps ensure that the adhesives on the back of the material will be better drawn into the fibers of the substrate to which it is being applied. Heat from both sides of the application helps ensure a better, more permanent result.

Purchase a cap press if you plan to print caps.
You will need a cap press with a rounded lower platen to properly print caps. Look for a press that has interchangeable lower platens, such as the Hotronix Cap press or Mighty Press. This is important because caps come in a wide variety shapes and sizes.

Do not use a home iron.
If you plan to produce garments with professional looking results, you must invest in a heat press. A home iron will not provide the consistent heat and even pressure that a commercial grade heat press can.