I have seen people hitting the gym and trying to build or tone those muscles from day 1.They either choose, or are asked to do exercises which supposedly would get them their desired results.
Here is something I figured out myself after years of working out.The first step when you start working out should be to feel, identify each of your target muscles. The work outs one choose should over a period of 7-8 weeks help him to thoroughly feel and isolate the target muscles.This means that after starting your work out, in a period of 7-8 weeks, one should be able to feel only his biceps move and getting the work out while doing a biceps curl, or feel only the middle and lower lats getting worked out while doing seated rows. Until this goal is achieved, I would say rest of the work out and time you invest would be a waste.
I derived a simple way of checking if I can isolate and feel a muscle.The technique is to flex that particular muscle in isolation.Now you would see that you could flex your biceps and triceps with out any difficulty. Try flexing your lower back muscles, upper back muscles in isolation and you would realize that its not as easy.Taking it one more level up, try if you could pump up your target muscles in isolation by working out that muscle with no weights or resistance, but a fictitious resistance. If you can achieve this, you can be assured that you have reached a situation where you can use resistance, weights or workout to hit the target muscle groups with out diluting or spreading the impact else where.
The objective of doing the aforementioned technique is to ensure that your target muscles gets the 100% impact of a work out you are doing. Else you are not getting the best of that workout and more over you will be more prone to injuries. So learn to focus, feel and isolate your target muscles during every workout. Master this in by 7-8 weeks of starting your training.