To be honest if u battle to pick up decent muscle then don't start cardio right now. If u are eating maintaince calories, lifting heavy ass weights and progressing each week in terms of doing more reps or heavier weight then u will grow nicely without adding on body fat. Remember in terms of progressing : say if u start a program write down all the weights and reps done for each exercise. Aim for 6-8 reps for the start of your program. If u aren't getting 6 reps then the weight is too heavy, if u are getting more than 8 reps the weight is too light. So after week 1 u will have a base line to work towards. For week 2 use the same weights and make sure you get 2 extra reps per set! So for example u do incline dumbell curls on week 1 and u use a 14kg dumbell and u get 6 reps in week 1, in week 2 push for 8 reps. That show u are progressing, in week 3 do the same thing but make sure u get 10 reps, week 4 make sure u get 12 reps. Now remember to do a 2-3 second negative and 1 second positive on each rep! It takes a bit longer but it puts more tension on the muscle making the exercise harder.when u are the bottom of each movement pause for a second so u take the momentum out of your training making it harder. For example when u squat, take 2 seconds to lower your weight till you are at the bottom position of the movement,pause for 1 second then explode up, then 2-3 seconds to lower the weight, pause then explode up. This will stop u from using shit form aswell as using momentum to get your weights up. If u can't do this with the current weights u are using then u are going to heavy and risk using sloppy form! Squeeze the muscle at the top of each movement. So when u are doing bicep curls when you lift the weight to the top position make sure u are squeezing the bicep.when u lower the weight flex your triceps as that will mean u are taking the tension out of the muscle and forces u not to use momentum to get the weight back up again...the 2-3 second negatives really hurt like shit!! but they really do take the sloppy form out of training and force u to use lighter weights and that means less risk of injury.