Create a throw away email address with oneof the free email providers. Save your primary address for friends,family and organizations you trust. Use the throw away addressfor contacting organizations you aren't certain you trust andfor "required" email fields in forms where they haveno legitimate reason to email you.
Consider using a disposable email addressservice that creates a separate email address that forwardsto your permanent account. If your disposable addresses beginsto receive spam, you can shut it off without affecting yourpermanent address.
Use a unique email address. Your choice ofemail addresses may affect the amount of spam you receive. Spammersuse "dictionary attacks" to sort through possiblename combinations at large ISPs or email services, hoping tofind a valid address. Thus, a common name such as jdoe may getmore spam than a more unique name like j75doe. Of course, thedownside is that it's harder to remember an unusual email address.
If you use Outlook or Outlook Express, usethe email filter to create filters to catch and delete undesirableemail. You can identify keywords commonly used in spam messagesand have Outlook send those messages straight to the trash bin.
If you only want email from a very specificgroup of people, and your email program has this feature, youcan accept email from only people on your approved list. Howeveryou risk missing messages from anyone who has a new email address.
If you create an account with a website orother service, make sure you check or uncheck the boxes offeringto send you "offers", "news", "updates"etc., unless you really want to receive that stuff.
Some spam has a message that says "clickhere to be removed from our mailing list" or somethingsimilar. Some unethical spammers actually use your click toconfirm that your email address is live and receiving mail andthey will send even more spam. Not all spammers do this, butenough do that I never click on the "Remove" link.
In some cases just viewing an email can signalthe sender that your email address is live and ripe for morespam. So if you have features in your email program that allowyou to turn off images and to preview mail, use them.