I have used a pump going on 8 years or so. Some pointers ( I was going to use the word, "Tips" but thought better of it).
Make sure you use a cock ring that will not dig into your skin. Some have a narrow band which can hurt like hell.
Use plenty of lube in the tube and around the edge. In the tube protects the base of your penis as it slides along the tube surface on it's way to erection. Around the edge insures a good seal. If there is not a good seal you are wasting your time.
I put the condom on before I pump. In my case, my cock head becomes massive which makes it harder to apply the condom.
Don't expect a large amount of seaman after you finish. I use a very tight band which will force most of my jizz into my bladder. Not a health issue.
Go slowly when you pump, take breaks so the blood can flow. Practice a few days before your appointment helps.
Going slow helps you protect your urethra. When I first started, I bused mine which hurt like hell for weeks.
Any more specific information PM me. I endorse the external pump whole hardheartedly. I have had a few providers tell me my cock head, being ultra hard than from a normal erection, is very pleasurable.
Good luck.