I don't plant both beds at the same time. Last year I even planted each 8' section successively. They didn't turn out very successive though as the later planted ones caught up to the early ones a bit as the weather warmed. This year the first bed was planted on May 28th. The second one was done yesterday June 17th. So about three weeks apart. I'm thinking they will end up being about two weeks apart as plants mature not based on the growing days, but on the GDD or growing degree days. And the weather is warmer in July and August than it is in June. I'm not sure if my guess is accurate though as I've never had a running total of my GDD for the year. Knowing your GDD is so useful as it can tell you a lot about when something will need to be picked or when an insect will start bothering your crops. My favorite GDD chart is from the Medina Beekeepers. They have one that lists the GDD of flower blooms times throughout the year.
This year I'm importing the data from my weather station into a spreadsheet and calculating the GDD. I've got one number on top that I can change that is the base number (the temperature above which the plant will grow). The base number is usually 40 degrees or 50 degress, but different plants grow at different minimum temperatures. I figure with a running total for each day I can figure out when to plant something like corn if I want successions to mature at a give rate. I remember planting peas last year in succession and three weeks difference in planting time only equated to a one week difference in maturity.
Once it was well weeded, I did the usual prep work. I fertilized fairly heavily since it was corn and squash. They are both heavy feeders. I don't really turn over my soil, but I do loosen it with a garden fork to aerate the soil. This time I didn't even rake it smooth since neither squash nor corn really need a smooth seed bed. I planted the corn in the middle 10' of the bed. I plant corn on a one foot grid. I put three seeds into each hole. I will thin them down to one provided too many come up and if there are gaps in the germination I'll replant once I see the others come up. I want two squash plants at the end of each bed so I planted three seeds where I wanted each of them. Unlike the corn, usually all the seeds come up with squash, but it never hurts to have backups.