Theres a lot of different theories on this mate.
At the moment I am cutting. I do not want to lose any muscle, I just want to lose bodyfat.
I lift weights for around an hour, do 5-10mins abs then I go for a 20min jog on the tredmill. I usually jog at around 8.8km/h and use a varying incline. You want to jog at a pace where you are just out of breathe and are able to speak. You dont want your heart popping out your chest. That would make you fitter but would also start eating away at your muscle.
Ive heard of people who just lift 3 days a week then have a whole session of cardio on the 4th day.
Its just whatever works for you best.