I've always flown by the seat of my pants with regard to my garden, but since we added so many beds this year, I decided it was getting beyond my ability to just remember where everything has been planted. I also thought it would be a good idea to consolidate all the tips and miscellaneous information I've collected that deal with things like spacing, companion planting, pests, or other problems, and planting time tables.
It's fairly simple to construct your own. I wish I could add pictures of mine, but our main computer is down right now, so you'll just have to use your imagination. :)
I bought an inexpensive, three ring binder and used dividers that have pockets on them to mark the sections. I use page protectors for everything so the paper is protected if I decide to take it out in the garden with me when I'm planting. The reason I use dividers that have pockets is so I have a place to stick notes, or articles if I happen to be out of page protectors. That way they are already organized and ready to file after my next trip to the office supply store, instead of sitting on a desk, or in a drawer somewhere.
I have the following sections in my notebook:
Garden plans - I literally draw the layout of the garden (you could use graph paper) and
write in where things are planted. I write notes on the back of the "map".
Things like, how a particular variety performed, or whether or not you
saw a benefit from a companion planting.
Tips - This is where I store charts for crop rotation, spacing, and compainion planting.
Pests - Info. on pest problems and organic solutions/suggestions.
Other problems - How to diagnose, and organically treat other problems that you may
run into, like fungal diseases or nutrient deficiencies.
Articles - Sometimes I run across an article that covers a wide range of information, which
makes it difficult to file in any one section. This is where those go.
I've seen many people talk about keeping a gardening journal and I can wholeheartedly agree that it is enormously helpful. If you're not already keeping one, it'd be a great idea to get one ready before the next planting season.