A thing I find important: make your garden suit your personality. Some people like straight rows of carrots or salads or other plants. Don't force yourself to have your plants march in a row like soldiers if you don't like it only because a book says you should have carrots next to onions or so. You could have them in clusters - or concentric circles or whatever. It should be aesthatically pleasing to your eye!

I'm a big fan of radishes for "blank spaces". Especially early in the season there's a lot of place between other plants and flowers - fill them with radish seeds. It's fast and easy to put the seeds and the radishes are ready to harvest in a few weeks. Often the plants have grown, otherwise the next generation of radishes can come. Any space filled with a plant we want is less space for the weeds we don't want ;)