Different persons need different types of workout and so does the various muscles in the body. These muscles need definite exercises which are done repeatedly so as to achieve maximum effect on them.
There are several basic exercises that target specific areas of the body that are being used by bodybuilders: for the chest, bench press; for the quadriceps, squat/deadlift/lunges; for the biceps, bicep curls; and for the calves, calf raises.
As one continually does these exercises however, it becomes dull and causes him to hit a plateau. In order to prevent this from happening, variations are added and this made doing these exercise routines more exciting and fun to do.
Variations of these exercises include:
• Flat or inclined bench pressing using a barbell or heavy dumbbells.
• Parallel, breathing style, front style, or regular squat.
• Barbell bendover and stiff legged dead lifting.
• Dumbbell and barbell curl, hammer curl, and inclined bicep curl, etc.
• Standing and seated calf raise, one leg calf raise, and smith machine reverse calf raise, etc.
For the lunge: the basic form is to stand straight with feet apart while holding a dumbbell, then place one foot in front of the other and bend both knees going as far down as you can, hold position for one second before slowly standing up into starting position. Variations of this exercise include:

• Rockin’ the Cradle which involves starting off in the basic lunge form and while one knee is almost an inch from the floor, the hips are raised while driving the left knee towards the ceiling and at the same time rocking the weight on the right leg.


• 
  Pass the Mustard which starts off in the same manner as above but with hands clasped in front, rotating hips and hands 180 degrees towards the right then switching into a right footed forward lunge. Reverse the process.


• 
  Single Legged Lunge involves placing a leg behind and resting it on a bench while holding a pair of dumbbells and bending the front leg to do a squat.

Simpler variations are:

• To put more force on quadriceps muscles, take a lesser forward step with the knees straight over the toes.


• To emphasize the hamstrings and glutes, take a bigger step forward making sure to keep your balance.


• To focus on glutes, instead of a forward step, take a side step.

These are only a few of the many variations that can be done while doing the lunge and the other basic forms of exercise. These modifications can help in making your training a more challenging and exciting one and prevent you from getting into a plateau.
To conclude:
These modifications will also help encourage you to continue working out and building up your muscles so that you will achieve your goal. Always bear in mind that hard work, determination, and perseverance will carry you through any hardships towards attaining whatever you desire, in this case, a perfectly proportionate and muscular body.