First thing is to have the right size tube – having a tube that is too wide will suck your balls in and make pumping uncomfortable.
Stick with 20 minutes of pumping every day.
1. Do a quick warm-up rub of the area with a warm, wet hand towel to get things clean and to get your blood flowing,
2. Use lots of lube to ensure a good vacuum seal (make sure to use a lube that doesn't damage the seal of your pump, i.e., probably silicone-free). If you're having trouble keeping a seal, look into getting a better seal, for example:
Optimum Series Universal Pump Sleeve
3. Pump until you're at full size, and back off (release vacuum) if you feel pain. You should never overdo the vacuum and you're obviously going way too far if you see bruising or blisters after pumping. If you see a blister forming, stop pumping immediately. It will take a few days at least to heal, so never pump to injury as it sets you back from making gains every time.
4. Take a break every 5 minutes (i.e., you're going to do 4 sets to make 20 minutes) by releasing the vacuum gradually, take your cock out of the tube, and switch hands each time so your ligaments are straight on both sides. This way, you won't end up pointing right or left because of using only one hand to hold the tube. This can also help fix that problem since you're straightening it every day. Repeat the pumping process above.
After you're done, do the same thing with the warm hand towel to clean off the lube and circulate your blood.
You don't actually need the ring, since the seal at the base performs the same function under vacuum. Some people like to use it afterward to keep the size, but if you're just pumping for growth (i.e., not before sex or showing off), you can leave the ring for other times.
Pumping for growth is a gradual process. You'll be tempted to increase vacuum pressure to make quick gains, but that always results in injury. Patience and consistency are the keys to permanent gains.