Depending on the wood you’re using, it can be a challenge to get good contrast without burning deeply. A trick someone posted on Facebook is taking a bit of baking soda dissolved in water and spraying it onto the wood. Let that dry and then try your engraving again (with lower power than usual). The baking soda reacts with heat and gives a much darker burn.
This is an example done with a 60w laser, and the settings are included: