How to gradually increase fitness?

Try snacking on sunflower seeds, as their great for your natural metabolism, also i've taken up running recently and its really helped, try running for slowly jobs for 20 minutes then turn round and try and do the same distance home in 10 minutes. Also, stop eating completely after 5.30 or so, the evening is when your metabolism is at its slowest. Do muscle work, this will again help with metabolsim, if u dn't want to build muscle the just use 1-1.5kg weights and do high intensity reps. Hope that helps!!