Think about it, if you keep the soil in your garden covered, there is less room for weeds. So what do you keep your soil covered with? Plantings of new crops! Plant a new crop as soon as you harvest a crop and pull up the crop that is finished. For example, you can have a cool weather crop in the ground now, and then pull up that crop as the temperatures rise and it's time to plant something like tomatoes or squash.
So what about relay planting? Let's say I have a cool crop in the garden such as cabbage and it's going to be ready to harvest soon. I can plant bean seeds next to the plants or slightly under the leaves of the plant a couple of weeks before you want to harvest. When you harvest the cabbage, you have your beans well under way and ready to fill in the space. You can do this again in the fall. In an area where you have something like squash, start putting in seeds for a new crop like lettuce or broccoli.
I plant lettuce, radishes, and carrots at regular intervals using the shade of other plants to get through the hot summer months and then when fall comes around you have a good foundation started for your fall harvest.