If you want to increse your ability to lift more weight you need to lift more wieght with fewer reps.
For strength gains I recommend 4-6 reps at maximum workable weight.
When I was training heavily and my weight plateaued I would do my normal sets followed by one or two sets of even further increased resistance(spotter is essential) for 4-6 reps. If the first set I could do 6 reps, I increased my weight again and exhausted at 4 reps for the second set.
For example Inclined Dumbell Presses
2 warm up sets, 15 reps @ 35 pounds.
1 set of 12 reps @ 55 pounds
1 set of 10 reps @ 65 pounds
1 set of 8 reps @ 70 pounds
1 set of 6 reps @ 75 pounds
Strength sets following above sets
1 set of 4-6 reps @ 80-85 pounds (decide by feel after last set of regular workout)
1 set of 4 reps @ 85-90 pounds
Add this onto your workouts to see some gains.
Also try to work on building the stabilizing muscles for the movement you wish to improve. For bench, this means anterior and lateral deltoids and triceps as well as your abdominals and lower back.