I use Clen, also use Tren, both of which are extremely hard on the system. You have to take support with these products or you will have problems. Well you will probably have some sides one way or the other, but that is just the nature of these drugs and you have to decide what you can live with.
Generally for Clen as a male you start at 20 or 40 mcg. You do that for a week to see how you tolerate it then you jump up to 40 or 80 mcg depending on where you started. As a guy from what I have read 160 mcg is the max you can go to, but I started cramping like crazy at 120 mcg and had to back off to 80 mcg and that is a level my body seems to deal with well.
While on Clen though you need 2 other things. First you need to supplement potassium. Clen will cause cramping at some point and potassium and water helps prevent that. Also take a multi vitamin, as an old guy I use one a day, but better ones probably exist.
Just be warned, by using Clen you are stepping into the abusive side of the steroid / body building supplement world. These are not things most people that are not competing would normally even consider taking.