As you are probably reading, it is best to leave a ‘rest’ day inbetween your weight workouts. This is because it takes time for your muscles to recover. It allows your body to replace the glycogen stores (the muscles energy), if you do not allow this, then because the muscle has no energy, it will eat itself, therefore becoming small and weaker. Working out 3 times a week is the best way to get into shape (ie, Mon Weds and Fri) and maybe a bit of low intensity cardio (like cycling) on rest days to get your heart pumping the nutrients to the muscles more.
Try using a barbell and dumbells rather than machines. This is because you use a variety of muscles to stable yourself when holding a barbell or dumbells. This helps build extra muscle and also builds up your core muscles (the foundations). From my training, I have found that increasing food intake is vital, not eating enough makes you feel tired and can ruin gains. I try to eat about 300 cals before a workout (30 mins before) consisting of some complex carbs and high quality protein in the form of a shake. This provides energy throughout the workout. After, I take another shake which provides my body with adequate nutrition to recover.
It is vital that you spend no longer than 1 hour in the gym, because you go backwards in building muscle from this point as this is when the glycogen runs out.
Also, to fulfill your potential, ensure that you work each body part (especially smaller muscle groups) only once a week to allow proper recovery. I use this cycle-
Mon – chest, back and abs
Weds – Arms and legs
Fri – shoulders and abs
To consistantly make progress, make sure that you add weight (about 3-5%) to the machine/barbell each session as you will end up hitting a training plateau otherwise.
To gain a lb of muscle, you must work out how many cals you require and then add 500 to it (the opposite of losing weight). goto to find out exactly how much your need.