Need help with printing preparation

I am very new at this. I am making some small cards and bookmarks and I just figured out that printing coulor might be different from what I see on my screen.

Before inserting cards into Corel Draw, I do preparation either in Adobe Photoshop or Macromedia Fireworks, because I am some familiar with those programs. Some images are CMYK and some are RGB.

I am not going to print it on my printer but take it to local graphic bussiness so they will do the printing. All I know about their printer is that it is digital.

So my question is... what is the best thing to do to prepare my work for that. And if there are some questions that I need to ask them in order to prepare it right, what are the right questions to ask?