There are two main ways how you can help fight spam:

1. First the easiest:
   Ignore it, delete it, never reply to it, never click any links in it, and above all never buy any product from a spammer. Mozilla Thunderbird has a spamfilter build in.
   

2. Second and the hardest:
   You can complain/report the spam to the spammers service provider, you can complain and report to the police some spams, you can ask your ISP to employ blocklists such as the SORBS DNS block list.

How will deleting or ignoring do any good you ask?

Well simple, the only way spammers make money is when spamming works.

Spamming works when you, the receiver, answers the mail by going to the company who ordered the spam and buying (or just enquiring about) a spammed product from them.

Not only that, but spammers can make money by you just clicking on the links in an email. This works in the same way that people make money out of you visiting their web site and clicking on an advert on that page.

Never reply to spammers

This proves your existence to them and you become a "valued customer" who will now be put onto email lists and sold onto other spammers for good money. You'll get even more spam.