Figuring out when to start seeds

So yesterday I started broccoli, cabbage, kale and cauliflower.  Next week I'll start other seeds, the next week others, etc...and I'm always hoping I get it right.  Last year I started seeds too early, it was such a cold spring and I estimated the seed starting dates wrong.  The cabbage and broccoli got weak and many died.  I also learned that I may have been starting them too early no matter what the spring was like.  I think this has been my biggest problem so far. 

I am keeping a calendar and writing in when I plant each seed, and this year I used "The Gardener's A-Z Guide to Growing Organic Food."  This book has descriptions of many veggies and herbs, and in the description it gives you the first seed starting date by telling you how many days to start the seed before the last day of frost.  You do have to know which seeds you start from seed indoors and which you direct seed, but it has that information too if you don't already know it.  It helped me a lot, and it's all a big experiment anyway.  It also tells you the last date you can start seeds, so you can succession plant.  I'll probably try to succession plant this year - especially in the pea location because they're done so early in the season.