It helps to have soil that warms up quickly each day. In the ground, that means well-drained, good tilth, not too wet. I've had very good luck with black plastic containers, 5 to 7 gal. depending on the size of the variety. A small plant like a Serrano or Tabasco may work better in a 5, and a big one like Yellow Banana in a 7. Any good bagged potting soil works fine in containers.
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In the ground, I dig in a mix of steer manure and bagged Kellogg's Amend, using enough to make the soil nice and light, (with my heavy soil, that usually means as much as would cover each square foot at least 4 inches deep--and more is better.) Sometimes I add some regular all-purpose sand (do NOT use the stuff that's been graded--unless you have both finer and coarser sand particles, you can easily end up with something more like concrete!) I usually dig some gypsum into the soil, too--the calcium and sulfur it supplies help. And a generous layer of coarse mulch on top after everything's planted is a good idea.
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Sometimes I just dig a moderate amount of any good tomato or vegetable fertilizer (I prefer the ones that list which micronutrients they contain) into the soil before I plant. I then pour some epsom salts (drugstore kind is just fine) dissolved in water over the plants every couple weeks to give them the extra magnesium they need. A drenching with a solution of a couple teaspoons per gallon is about right.
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I've also had very good results with Miracle Gro Tomato Food, which has the right amount of magnesium in it, about once a week. augmented with an occasional leaf spray of calcium nitrate. I use about two teaspoons of the 10% liquid per gallon of water once every couple weeks or so. This prevents a "seersucker" puckering the leaves tend to develop. Since the calcium nitrate concentrate I use also contains about 8% nitrate, this also gives the plants a little shot of instantly usable nitrogen. Don't go nuts with this--if the seersucker leaves stop forming, you can back off.
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The other thing is tip pinching. Pinching out terminal buds forces growth down lower, making a bushier plant. I've also had peppers--especially when I was a little late planting them--start flowering and fruiting before the plant's grown very much. When that happens, I keep pinching out flowers and fruit until the plant is bigger. Don't sweat the loss. In the end, I think I've gotten even more peppers by doing that. Here in L.A., I had a Caribbean plant a few years ago that was still cranking out dozens of beautiful, deep-red habaneros  well into November.