Etiquette says that you can send out a pre-wedding gift thank you anywhere from immediately to two weeks and for wedding gifts/post wedding gifts you have up to three months to send them. My suggestion is that you make a goal after the wedding to write 3-4 thank you cards a night. Your husband should also be part of the note writing, it's not just the bride's job. Also, if you write the thank you notes to your friends and family, and he his, then it'll be easier and more enjoyable. You'll see that I highlighted the groom's names (yesterday's image) to assign who has which cards. Between you both, you'll be able to get out your thank you cards in no time.
You don't have to write a lot- 3-5 sentences will do. It should always be personal- a computer printed note with a prefab message is a big no. Identify the gift given by individual guests. Then you can write about how you appreciate it, or what personal meaning it has for you, or how you plan to use it. Even if you'll be returning the gift never mention that in the thank you. If you were given money you don't need to name the amount specifically but it's a nice touch to say how you'll be using the funds.
Finally, end your note by letting them know you appreciated them attending the wedding. Only one of you need to sign the note but it's always nice to mention your partner "...Lauren and I both appreciated...sincerely, Joseph."
Photo courtesy of Martha Stewart.