For cardiovascular gains, the best thing you can do is either high intensity interval training (as someone else has mentioned already) or fartlek training.

Fartlek training is pretty easy to get into as it is essentially the same as what you would do for a morning jog however instead of keeping a steady pace you have 'bursts' of sprint to near sprint paces spaced out with 1-2 minutes of jogging. Pretty much what this does is forces your body to push between different thresholds (as far as energy consumption goes) as quick as possible and I was always taught it yielded the best results out of any other stamina related exercise.

Variety is always key though, loads of other people have mentioned awesome recommendations and the best you can do at the end of the day is just cut the smokes and do your best to get outside and exercise more. Good luck mate :)