Most cool weather crops, brassicas especially, do better in the Fall and it is time to start planning now. A handy gadget I bought a few years ago is Clyde's Garden Planner. I don't remember where I bought mine, but Amazon has one (link in my sidebar on the left). It's a slide chart, so you can see everything at a glance. It is formatted in a "time phased" format so that it is possible to see at a glance the entire planting, growing and harvesting period. It shows proper indoor and outdoor planting times relative to spring and fall frost dates for several common garden vegetables. Since frost dates vary from region to region, the chart will slide, making it useful in most parts of the northern Hemisphere where frost is a critical gardening factor. The front of the chart shows the spring season, and the flip side acts as a guide for fall gardeners. Frost dates are included in the directions.
If you do not know your average frost dates, you can find your dates by zip code at Dave's Garden.
The most important thing right now is protecting seedlings from the heat. I have started some carrots in an area that gets afternoon shade from the larger plants around it.
If you plan on cabbage, Brussels sprouts, kale, cauliflower or broccoli, seeds should all be sown soon, late June-mid-July in most areas. Depending on what squares I have open, I set up a "nursery" & make a seed bed in the garden, but usually plant in pots. I let them germinate in the shade, but after that I keep them outdoors so they get at least
5-6 hours of sunshine daily,, with afternoon shade. Just be careful not to let them dry out - this can happen quickly.