Whoa...2500 dpi is WAY too much! I hardly ever scan at anything more than 150 if I'm not going to run any prints. Print is a whole other issue...
Make sure you have a clean and CLEAR image to start with. After the scan, spend some time in Photoshop (or any respectable photo editing tool) working on cropping, sharpening, and color adjusting. Most consumer level scanners are crap, and I always end up spending lots of time in Photoshop trying to get the image to 'pop' as much as I can.
It takes practice. When Johan suggests you take a look at the 'great shots' section, he means it. Take a LONG AND HARD look at the quality of the images in there and compare them to yours. A good test is to examine the text anywhere in the image...is it smooth (not jagged?). Can text that is far away be read clearly? Look at the grain in the image (especially the shadows)...the entire image should be ssmmmoootthhh. No grain!!
Like I said...it takes practice. Maybe try posting your image here (or at least a link to it) so others can see it and offer suggestions.
Good luck...and KEEP TRYING!!! The best way to learn is for someone to tell you "you're not good enough". Prove 'em wrong!