I think the biggest reason my vegetable garden isn't more productive is the soil. I've read that good soil should have about 5% organic matter and mine's nowhere near that (many western soils only have about 1%). The easiest thing to do is dig in bags of organic soil ammendments, but that's also probably the most expensive way. Nonetheless, I added 8 large bags this Spring (and about twice that last year) and some places are a little better, but it hasn't made enough of a difference.
Last fall and in between plantings I dug in as many leaves and kitchen scraps (plant matter only, of course) as I could. They seem to break down pretty fast but I'm still not seeing much visible improvement so I'll keep doing that each fall. I never have to mow the lawn (one of the perks of your wife running a landscaping business) but I'd like to get my old mower running again so I can chop the leaves up first. That way they should break down faster.
I'm also trying composting again. I tried a compost pile in Utah, but I don't want an unsightly pile in the yard. Besides, it took forever, and I wanted to see if I could speed it up. I've read about compost tumblers that promise perfect compost in 2 weeks but they cost $300 to $400 - and if I were going to spend that much I might as well spend it on bags of soil ammendment. (Also, I'm a little suspicious of the claims those companies make.) So I found a basic plan online for making one, and with a trash can, some scrap wood and pvc pipe, and a few hours one Saturday afternoon I made my own.
The stand holds the trash can up so I can turn it around once a day, mixing everything inside. The pvc pipes, which run through at different angles, break everything up and have slits cut in them to allow oxygen to mix in when it tumbles. Unfortunately, I used pretty large pipes which seems to dry it out faster, so I've covered some of the ends. The lid stays on even when it's upside down. And it's on the south side of the house where it gets plenty of sunshine to help heat it up. It's not as pretty as a commercial one, but the price was right.