OK.. this will be a long one.. read on…
First and foremost, understand that being an affiliate requires persistence & work in all of its forms.
If you go for a website – You will need to do research (Keywords, design and call to action content), you will need to sacrifice (for a good cause) time, and eventually you will have to spend some money… once you realize & accept these, you’re already in the right direction and ready to go forward.
Research & research (and research):
First, understand the basics of affiliate marketing. Don’t skip this stage and rush forward.
Understand terms such as PPC, CPM, Pay per lead & LEARN pay per sale (CPA / Rev-share %) into detail.
It will give you an edge later on when you will (hopefully) look for side-ways to promote your website. (That aren’t SEO).
Then, understand what you want to do, what you want to promote & HOW you want to promote it.
Do you want to collect email addresses? Or you want to build a traditional affiliate reviews website? These are critical when you engage design and keyword research.
More on research……
• Use google to learn from veteran affiliates (but don’t copy content..).
• Participate in forum discussions, and be involved in the industry.
All of the above are much more important for newbie affiliates than backlink tricks and quick SEO tips (in my opinion… atleast).
When all is ready, find the affiliate program that suits YOU:
If you have German traffic, you should pick a program that promotes a casino that is strong in Germany. (appropriate website language, appropriate Client, and the Appropriate payment methods). The conversion rates will be higher if you have the right tools.
Understand how online casinos and poker rooms work, what are the revenue-models their programs offer, and how is revenue collected (CPA baseline, Revenue-share negative carryover – YES OR NO?).. this is very important.
Does anyone reply your emails?
If you signed up, and got a welcome message a week later, you are probably not at the right place.
Is the affiliate manager helping you in person? Do you get personal treatment or you get a blast of general email templates with 4 different fonts caused by outlook copy pastes? I have seen things (NONE from CAP certified, to clear the air).
Finally, many affiliate managers were and still are affiliates (to some degree).. and that’s a good stop for assitance.
Finally #2 .. don’t give up.. it’s fun.. 
Cheers.