I'm an avid weight trainer and have been for over 10 years.  I have trained with some of the best in the industry.  Here are some basics that every bodybuilder follows:
If you are trying to build lean muscle mass you must first make certain that you are consuming more clean calories than your body is using.  If you aren't, you will never actually gain.  Once your diet is established, then focus on your supplmentation, training, and rest.  
I would recommend:
Day 1 - Chest/Triceps
Day 2 - Back/Biceps
Day 3 - Off
Day 4 - Legs
Day 5 - Shoulders
Day 6 - Off (maybe abs, calves, cardio)
Day 7 - Off
You can work in calves and abs as you see fit.  If you have a tendency to be skinny, I wouldn't do any cardio at this point.  
I would do about 4 exercises per body part, 3-4 sets per exercise, and 6-10 reps per set.  If you can do more than 10 reps, you should probably increase the weight.
Your workouts should be kept to 1 - 1.5 hours per day.  Any longer and your body has a tendency to go catabolic.  You must be careful not to overtrain.  
You should be eating 5-6 meals per day or approx. every 3 hours.  You should be consuming 1.5 grams of protein per pound of your body weight and about 100-120 ounces of water per day.  Water is very important for muscle growth.  This type of diet isn't easy and requires a lot of preparation, but if you follow it you will make good gains.  If you don't, you won't.  It's that simple.  
Good luck.