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A great way to gain desired strength in your muscles is to keep to (generally) the same routine for 3-4 weeks. Specifically, the same exercises utilized for that time period, with differences in weight and after each week.
For example, if I decided to perform a standing shoulder press for the month, I would start the first week with 20 lbs for 20 reps. The second week, 25 lbs for 16 reps. Third, 30 lbs for 12 reps. Then finally, 35 lbs for 10 reps to finish it off. This would help my body get used to the motion, allow my other muscles that stabilize me to get stronger, allowing me to continue to increase the weight.
Now, this is not the only way to do it. You could also keep increasing the weight while keeping the same reps (probably in the range of 10-12). But all in all, if you keep the same exercises for a few weeks, you will see strength gains in your muscles with those motions.