Try to enter erect or in range of 70-80 % erectness. Don't go for a long time as it's your first pump. Read about the
5x5x3 protocol, which in the beginning might be more like 3x3x3, you don't want to get overzealous!
In the beginning it's better to do short sessions, to get the hang of it; your body should signal when it's too much. Too hard or too long in the tube usually means fluid retention (donut head) and more red spots which can be deeper; discoloration might occur.
I'm not trying to scare you here, [words=https://officialhydromaxpump.com/?uid=6&oid=2&affid=98]hydropumping[/words] is fantastic! But go slow, go long; it's a marathon. Some red spots usually occur, but they should fade away within 24 hours. Basically that's a [words=https://shop.mattersofsize.com/products/sizegenetics-penis-extender]sign[/words] of some "new blood" from what I recall reading, but as said, they should fade within 24 hours or so.
Don't be scared; fluid retention will probably happen and it'll go away. For gaining purposes it's best to try staying with minimal fluid retention. So, as said, the
5x5x3, in your case go for 3-5 minutes in the pump, see how it feels.
When you've got used to the pumping and the sensations, you could / can order the Vacu-vin kit and modify the pump for more power.
Have fun pumping, remember to check DLD's [words=http://www.mattersofsize.com/forum/showthread.php?64036-My-Best-Work-Ever-Penis-Enlargement-will-Be-Changed-Forever-gt-gt-Gain%20inches%20with%20SRT-Theory-and-Routine]
SRT[/words] thread, read about the
5x5x3 program and Slow Squash Jelqs. Knowledge is power!