I've been promoting affiliate programs for a while. One thing I would recommend is to choose those programs that you truly believe in and know are good products. Then you can genuinely endorse them with confidence. You don't have to have used the products yourself, but it certainly helps.
I also think you should try and find programs that give you a solid commission per sale. One reason is pretty obvious: more money! There's another motivation: if the commissions are subtantial it will take less time for you to reach your payment threshold. So you'll get your money posted or e-mailed to you sooner. Once you've got this cash in your hot little hand you then know for sure that the merchant is reliable. You then have confidence that all your subsequent efforts will be rewarded.
That said, it can be hard to actually make sales with programs like this for various reasons. Maybe it's a very small proportion of leads that you refer that actually converts. Or perhaps the market has changed, and something that used to convert like crazy doesn't do so any more.
I've found that this last scenario applies to a couple of programs I've been promoting. That's why I'm now getting into pay per lead affiliate programs. In these, you just have to get people to sign up for information, or join the free version of the site without actually upgrading. That's a much lower bar, of course.
Not surprisingly the commissions are much smaller. Still, there are some programs out there that reward you well. Clix Galore, Commission Monster and Check My Stats have some good pay per lead programs with generous payments. They are definitely worth checking out if you are an affiliate marketer who gets lots of Australian traffic.