Hooping - Overview – MELCO Help Center

Here are YouTube videos about proper hooping techniques:

Make sure the hoop arms are attached securely to the machine. If you can wiggle the hoop arms side to side, they are too loose. You can also upgrade to new High Performance Hoop Arms.
Choose Round Hoops whenever possible, they provide more even tension than other hoop shapes.
Pre-Tension the hoop screw. Watch Hooping Tension and Technique for more information.
Select a hoop that fits as closely as possible to the design without going over hoop limits.
Check how the garment is hooped; the garment may be hooped too loosely. The fabric should be very taut in the hoop, similar to a drum, to prevent Flagging.
Depending on the fabric, if it is slipping in the hoop, you may need to wrap the bottom hoop with a fabric, “seam binding.”
When you slide the hoop underneath the bracket clips, both sides should snap securely into place. If either side of the hoop can move front to back or is not seated underneath the clip, the hoop may move during sewing.
Review the weight of the garment being sewed. If you are sewing a particularly heavy garment, try sewing at a slower speed to see if thread breaks become less frequent. Furthermore, if there is an abundance of material hanging outside the hoop, be sure it doesn’t become tangled in the machine.
Make sure the hoop isn’t hitting the needle plate. It may be that the hoop arms and/or the hoop itself have become bent downwards. As a result, if sewing very close to the hoop perimeter, the hoop may hit against the needle plate causing a thread break.

Here is more general information about hoops:

Here is more information about hooping and loading Caps/Hats:

Here is more general information about Embroidery on Caps

Here is more information about hooping for other specific applications:

Here is more information about different styles of hoops and clamps: