The following is the most basic method of gaining strength that I know of, and it will work forever.

It's called "working up" to a weight. Say you're going for five reps on an exercise, and you want to use 300 pounds (this assumes that last week you got 290-295 for five reps, or 300 for four reps). You could work up to it like this:

135 x 6
185 x 5
225 x 3
275 x 2
and finally 300 x 5

Working up is basically an extension of warming up, so none of the sets prior to your first set with your goal weight should be fatiguing (these don't even count as sets in your workout).  You want to keep the reps low and increase the weights every set so that your central nervous system gradually gets used to the idea of lifting that very heavy goal weight. The amount of weight you jump between sets is really dependent on how much you're ultimately going for, but I'd say increasing by 40-50-pound increments is usually fine. Note that these don't have to be exact. If it's easier to load a 25 plate than two 10s and a 2 1/2, go for it.

This method works best when working up to low-rep sets, but you can employ it in any rep range. Sets of 10 or more reps simply won't require as many work-up sets as a set of 5 heavy ones will. In that case, you might only perform two sets of 6 reps before your work set of 10. Still, keep the reps low, as you don't want any lactic acid buildup in the muscles before your first work set. The whole point is to prepare your body but still feel fresh for the first heavy lift.

Do not confuse this process with pyramiding. Pyramid sets, in which you often perform 12, 10, 8, 6, and maybe 4 reps for an exercise aren't very effective. Because every set is taken to failure or near it, they tire you out before you reach the heaviest set, which you need all your focus and energy to perform well. This is also the set that will do the most for strength and muscle growth. This isn't to say that you shouldn't perform higher-rep sets, but you'll generally want to save them for after your heavy work, such as in this example. (They're called back-off sets.)

Work set 1: 190 x 4
Work set 2: 190 x 4
Back-off set 1: 165 x 8
Back-off set 2: 150 x 12

Give it a shot.