I don't know why it took me so long to figure this out: Don't be afraid to write in your cookbooks! I guess I was afraid to write in them for a long time. Grandma always told me to write things down about a recipe. It took forgetting important things time and time again before I got this figured out.
When I try a new recipe I like to write down what I liked about it, what I didn't like, what went well, what I could do better next time, even write down if the recipe is worth making again. This is a much easier way to keep track of things than trying to remember them. Besides I think it's really fun to go back through a cookbook and see what your first impressions were of a dish that has become a favorite, or how you have modified a recipe over time to fit your needs better. Thanks for a good tip Grandma!
Just as a side note: My grandma is gone now, but I find great comfort in looking at her handwriting. It makes me feel like she is in the kitchen with me. She also taught me that when someone gives you a recipe, keep it. You will enjoy looking at a loved one's handwriting someday, even if the spelling is not that great!