If you've started to monetize your blog, or are thinking about it, you've probably already considered affiliate marketing as a primary income stream, or even your ONLY income stream. After all, all the bloggers are doing it, right? Affiliate marketing isn't for everyone, but it can be a good way to earn some money blogging. Before you even add ONE link, though, you should know what you're getting into and how to deal with issues that may arise.
First, do your research on affiliate programs, decide which ones you want to work with. This post on How to Get Started With Affiliate Marketing is a good overview of how to choose and what to know about the most popular ones, and a good place to start.
I would suggest you also to ask other bloggers who use the programs what their thoughts and experiences are. And Google is your friend. KNOW what you're getting into before you enter into a business relationship (because that's what it is) with any company; you don't want to be surprised at any point because something “un-expected” happened.
Read TOS carefully, know what minimum payouts are (sometimes you won't get paid if you earn less than a certain $ amount a month), what your responsibilities are in terms of paid search, and keeping your blog going, or displaying coupon codes, and how you should behave on your blog as a partner. Also, find out what happens if there's a reporting error, or site down-time and your clicks/sales can't be tracked. Who do you go to? What recourse is there for any problems or issues you may have? KNOW all of this before you start using a SINGLE affiliate link.
Of course, you will have to apply and be accepted to any programs you want to join. Each one has different qualifications for acceptance, though, so you may not be able to join all the programs you're interested in. Be patient and apply again once you're more established. Blogging is like any other business, it takes time to prove your value to companies you want to partner with; you may have to work your way up before you're taken seriously.
Something you should also consider is whether you want to work directly with an affiliate manager for each company or if you'd rather work with an “aggregator” like RewardStyle, ShopStyle or Skimlinks. You'll get an account manager with those companies and they'll handle everything with regard to your account, but with the large affiliate companies like Linkshare and CJ, for example, you will work directly with an affiliate manager for each program (i.e. Nordstrom, Shopbop, etc.) and they will communicate with you directly. You have to apply separately for each program, though, as opposed to RewardStyle, where you only have to apply once and you're accepted to all the programs they work with.
In the case of tracking errors or payout issues, it may be easier to deal directly with an affiliate manager instead of an account manager (i.e. RewardStyle, etc.) because they usually work with just one program. On the other hand, it may be better for you to deal with only one person for any issues that may come up. You'll have to decide which you prefer, and the companies you feel most comfortable with.
I use a combination of direct affiliate programs though CJ, Linkshare, etc., and RewardStyle, ShopStyle and Skimlinks, and have for many years. I started with the “traditional” affiliate companies like CJ because that's what there was. I still use those companies for several programs I work with because I've negotiated a higher commission rate directly with them than I can get anywhere else. In some cases, RewardStyle or ShopStyle offers higher commissions and in those cases I used those programs. I also appreciate the tools & widgets they have available specifically for fashion bloggers, but again, there are a lot of options for you nowadays, you're not beholden to only one company.
After you've looked at all the options, it's up to you to decide what's important to you and who you want to work with. Just because you're a fashion blogger doesn't mean you HAVE to work with RewardStyle, for example, they're not the only game in town, and in some cases, you can work directly with a program and earn a higher commission. You will have to research that and decide what's best for you. Then, it's up to you to monitor your account and make sure you think everything is running smoothly.