For example, if you had the intention of developing more Power then there would be not much reasoning behind 10-20 repetitions as the basis of your weightlifting routine.

This and the factors listed below should give you a greater understand of how you should be training. As a result, this understanding should bring you towards your goal as efficiently as possible.
Rep Range

To build
pure muscle mass then the reps should be kept in the 8-12 range. This
is proven
to be the optimum zone to make gain maximum muscle provided a
good form when lifting
the
weight is employed.
Type of
exercises
Compound
exercises for the major muscle groups such as Bench press to build
chest muscles,
squat for
legs and shoulder press for the shoulder muscle are the main muscle
builders.
Therefore, 2-5 compound movements should always be included in your routine.
They may not target your whole upper body like compound movements but they can be effective when hitting areas such as the inner chest, lower abs, calves, gluteus etc. Machines and cables are usually the most effective in this department.
Rest period
Intensity
should be the order of the day when trying to build muscle mass so no
more than
40 second should be taken between a set of exercises. Fatigue is often
the best
indicator of an effective muscle building workout.
Speed of lifts
The speed of lifts is one of the most disregarded
things for people who are
aiming build muscle Fast. Slow speed on the decline phase of your lift
will
help stress the muscles more thus breaking down the muscle more. Try
like so;
Declining for the duration of 4 seconds—inclining for 1 second.
Duration of Workout
No more than
50 minutes to prevent muscle breakdown.
Sets
6-9 set per
body part. Aim for 4-5 sets with the heavy compound movements and then
set
aside the rest for the isolation movements.
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Rep Range
In this
instance the rep range should be in around the 2-6 range. 4-6 if it is
an
aerobic sport you are trying to build strength, speed and power for.
For
example, football, rugby, basketball, etc.
Type of exercises
Power
Cleans, Power Jerks and Snatches are proven to be the best movements
for building
physical sport performance as they requires a combination of power
(strength
and speed) and flexibility.
Rest period
1-2 minutes
rest periods between power lifts. 40 second between the lunges,
shoulder
presses and dumbbell rows.
Speed of lifts
Olympic
lifts require speed when lifting the bar back upwards. This will in
turn
improve overall power.
Duration of Workout
30mins to an
hour and 15mins is the optimum time.