When do you want to get started?  If you are just starting and have no audience then some of the programs may not accept your application to become an affiliate, while others will let you get set up in minutes.  If you want to get started straight away then make sure you’re applying for programs that are less restrictive. Generally the larger, network style places will enable you to get going quickly while specific niche programs may require you to have a certain audience size or characteristics.
An additional note that must be made at this phase is: do keep in mind the LTV or the life-time value of your customer here. In certain scenarios (e.g.: subscription-oriented affiliate programs) it makes sense paying significantly higher commissions on the customer’s initial payment to the company when the latter knows that they will make much more (from the same customer) on future payments. More about it later in this text.

Affiliate networks offer you access to multiple (and by multiple, we mean hundreds if not thousands) of individual affiliate programs. They basically work by simplifying the signup process - instead of applying to become an affiliate for a each product you want to promote, you simply apply to join the network and instantly have access to hundreds of different affiliate offers.