I always go through the seeds I currently have, before cracking open my catalogs. It helps prevent buying duplicate seeds. Making a list of what I'd like to can/dehydrate also helps when browsing through the catalogs(I might not have remember to get cilantro for my salsa this year). Then I scour the catalogs to see what I want, comparing prices between companies, and make a list from there.
We use graph paper to chart out our garden space. This is a helpful way to see just "how much" we can plant. It's easy to get eager during the cold months and buy more seeds than you can reasonably plant in your allotted space. Gardening is a lot of work, so it's important for us to keep things as manageable as possible. This prevents us from being overwhelmed by weeds, bugs, and diseases that can really hinder your overall production.
On another note, a member on the Homesteading Today forum pointed out a great tool for planning the garden. It's a chart that allows you to enter your last frost date, and it figures planting dates for you! It makes things that much easier, plus you can print off a copy to keep in your gardening notebook! The seed starting chart can be found HERE!
We just had some windows in the house replace a few weeks ago, and kept all the old window panes to create some inexpensive cold frames to start seeds, as well as extend our harvest throughout the fall and winter. Once we get those started, I'll post our progress and hopefully some of my readers can get some ideas to help out their garden/food production around their homesteads!