If you are printing yourself, the most common cause of dark prints is a non-calibrated and/or too bright monitor. To get accurate prints rqeuires either a lot of trial and error or a good monitor which can be calibrated. I run my monitor at 80CD which gets me close to a print.
Getting accurately colour matched prints is not easy. You need to calibrate both your monitor and your printer if you want accurate colours etc. There are expensive and relatively cheap ways to achieve this and it's best if you Google 'getting accurate prints or print colours' etc to find resources to help you.
A surprising simple trick to reduce this frequent "my print is too dark" problem is to edit on screen with a white instead of black background when processing for printing. Having that blinding white screen border will give you a better reference for what a reflective print is going to look like - especially if you've got your monitor too bright to begin with.