I've been reading about a concept called square foot gardening. It challenges the traditional row planting, arguing that by planting in a grid formation, space is optimized allowing for a much higher produce yield.
Last year I was busy with other things and so I instead of measuring out the grid I used the highly scientific eyeball method. It kind of worked. I was able to increase the variety of my plantings while still getting extra tomato plants in.
This year I took it to the next level, I made templates! Using a scrap piece of plywood, cut one foot squares. Measure out standard planting grids. 16/9/4/2/1 (I combined 2 and 1 and made a single square with 3.) After drawing grid. I used a hole kit to drill large holes to plant through.
If you want to try, this website lists how many seeds per sqft for any given vegetable. As well as lots of tips on planning.