1.) Grow tall varieties if you have room. Shorter pea varieties are cute, but they are not as productive. I've grown many pea cultivars, and the most productive have been Mammoth Melting Snow Peas and Miragreen podded peas, by far-- both tall. I couldn't find my leftover Miragreen seeds this March, so I planted Little Marvel, which is a solidly tasty and productive three foot pea, but nowhere near as productive, delicious and heat tolerant as Miragreen, which reaches five feet. And the Mammoth Melting Snow peas have produced a quart a day for the last two weeks-- enough to hand out like zucchini in August! They are so tall and heavy that the vines tend to fold over at the top, but they keep on producing. (note: I initially thought Miragreen and MMSP were hybrids, but they are not, they are just superior open pollinated varieties).
2. ) Prep the soil. Manure, deeply dug a month before, makes a difference.
3.) Use inoculant. Yes, it costs $5 every year for a small bag of fresh inoculant, but bacteria are living things, and you need to buy them fresh every year. Legumes make a lot more of their own nitrogen with the help of the bacteria in the inoculant.
4.) Water well in hot weather. Peas like cool weather, but many varieties can survive a short hot spell if their roots don't dry out.
5.) Pick every day. If you don't the plant thinks it has done it's job of reproducing and stops or slows down blooming.
6.) Give them good support. Yes, lots of books say just stick some twigs in the ground for them to climb on. Phooey! That may be quaint but it won't be productive. Peas need a strong vertical structure to grow up. A tall, narrow planting is easy to harvest, especially one you can reach into from multiple sides. And the tall varieties I prefer need lots of support.
7.) Plant peas close together. They don't mind two to three inch spacing!
Pretty simple stuff, but it usually works.
Here are some pictures of this year's pea crops, in order over time.
Little Marvel:
Mammoth Melting Snow Peas:
Amaranth: