Once you start to see your mailing list grow the last thing you want to do is start sending out emails promoting other products every day. It's a sure fire way to get people unsubscribing at an alarming rate.
By all means, send them information on something that you want to promote, but first you need to warm them up. Start building that relationship. Sending them useful information will do you wonders.
Not charging for information that your readers can use is showing them that you are one of the good guys and not likely to start selling to them at every given opportunity.You can always send them some great information and let them know that they can always get further information at such and such place and offer them your affiliate link.
It can be a really great feeling to spend a few minutes creating an email and then sit and watch your commissions start rolling in, but I can guarantee you that if you do this too often, you wont see many commissions, but will instead get loads of emails from unsubscribes coming through.
If you treat your list with respect, the same way that you want to be treated then they will always be looking for your emails. They will soon get to know that you are sending them quality information without selling to them.
This way, when you do send them something that YOU genuinely think will benefit them, your response rate will be far higher than anyone else's.