What I've found out as a relative newbie is that mug pressing is not an exact science. This is what I've discovered - mostly the hard way, but also from reading on this forum.
Generally, I've found it better to go for a lower temperature and shorter time rather than increasing the temperature and time. Generally I'm pressing at 170c and 120 secs. Although I've recently gone down to 90secs. This is AFTER allowing the mug to heat up to 170c, which could be another two or three minutes.
Some advice on the internet says 200c for 5 minutes. This is WAY too hot and long. Although part of the 5 minutes may be heating up. But 200c I've found is way too hot.
If your temperature is too hot your black colour will look brown and other colours will start to look washed out. You can also tell if your temperature is too hot if there is a lot of burning/browning on the back of your mug paper
Fading at the base of the mug and towards the handle. This is caused by colder temperature at the base of the mug and towards the handle. It's harder to heat up the base because the base acts as a heat sink drawing out the temperature. Similarly with the handle. It's also near the edge of the mug blanket.
The temptation here is to increase the temperature. Don't. Best idea is to heat up the base of the mug before putting it in the press and/or put the mug as high in the press as possible. I heat up the base by holding it directly above the press as the press is heating up. But others have suggested warming it on a hot plate (cooker). I'm not sure what the solution for the handle issue is.
Colour bleeding, blurring after pressing and whilst cooling down. I've been getting this a lot recently. Just when I thought I had got on top of any printing problems. I think this is due to the mug still being hot and sublimation continuing after removal from the press. The ink spreads out and causes the blurring/bleeding. I get this particularly at the front of the mug (opposite the handle). I think it is linked to too high a temperature. On my press, I suspect that the area opposite the handle has a higher pressure on the mug than the sides. This increases the temperature towards the front.
The solution suggested by people on the forum to deal with bleeding is to quickly cool the mug by dunking in warm (not cold) water to stop the sublimation process. I haven't tried this yet. A bit scared of plunging a hot mug into water. But will give it a go and report back.
Inks: I started with sawgrass inks but the price is way too expensive. I tried out refillable inks from cityinkexpress and I can't really see any difference - so I'm happy.
Probably the most important thing I've learnt is lower temperature is best. Someone on the forum has stated that sublimation starts at about 150c, so pressing at 170c should be hot enough. Some people on the forum say 175c or 180c. At 180c I find I'm getting problems with being too hot. But, of course, that could be my set up. The rule of thumb is that if blacks look brown then it's too hot.
There is a sweet spot on the mug for your design that avoids most of the problems you will get. This is on the side away from the handle, front, top and bottom. This is where you might put a straightforward company logo type design. So if you tailor your designs to stay in this area it will make your life easier. But that is quite restrictive - and I tend not to.