Can't help you with squat as I've never had a bad plateau on that lift. I can help with bench though. I've found that what helps to break a plateau as far as 1RM (which I'm assuming you're talking about) is to throw in some high rep training also. It's helped me raise my max 40 lbs in a matter of a couple months. I'll just use what I've been doing as an example:
I bench twice per week, usually 2-3 days apart. One of those days I focus on high reps and burnout, the other day I never do more than 5 reps other than my warmup set, and go as heavy as I can.
For the high rep days, I will do sets of 15, 12, 12, 10, increasing weight each time obviously. Then after my set of 8 I'll raise the weight one last time and usually only am able to get 2-3 reps. Then after all this, I go back to the weight I had on my set of 10, and rep til failure. Then for the last set, I go back to my starting weight that I did 15 with, and go to failure, usually shooting for 20 reps. To easier visualize it:
Warmup set
15 x 135 lbs
Working sets
12 x 185 lbs
12 x 205 lbs
10 x 225 lbs
? x 245-275 lbs depending on how I feel that day
Burnout sets
AMRAP (as many reps as possible) x 225 lbs
AMRAP x 135 lbs
My max right now is 285 so obviously tailor the weight according to what you are able to do. You should be able to hit each of the reps, but don't make the weight so light that you don't even break a sweat. By the last rep of each set I'm struggling to get it up, but I do. Think of it as riding the fine line of going to failure without actually failing.
Then on the heavy bench day, I warmup with a light weight x 10 reps, and jump straight into the heavy weight. I'll aim for 5 sets of 5, but usually by the 3rd set it gets so heavy I can only get 2 or 3 reps, and from there I do singles until failure, increasing weight each time by about 10 lbs. So:
10 x 135 lbs
5 x 225 lbs
4-5 x 245 lbs
2-3 x 255 lbs
1-2 x 275 lbs
1 x ? lbs til I can't go any heavier
Basically the point is that I've found offsetting heavy low rep sets with lighter high rep sets is beneficial to raising your strength. The hypertrophy of the higher reps builds more muscle mass, which doesn't raise strength in and of itself, but gives your body more to work with when you do decide to train heavy. I've always been a fan of blending bodybuilding and powerlifting parameters for lifting.
