First, find the spots on your concrete floor that aren't level. For a rough-and-ready project, you can use a float board and scrape it along the floor, watching for any spaces. The float board can be a simple plank without any warping, as wide as one of your slab sections. Of course, if you have a level handy, this can work well too, as can a piece of string -- pull the string taut on either side of the slab and slide it along like the float board. This step works best with helping hands, so you can measure the surface and mark the areas that have particular problems.
Leveling compounds are products that help smooth out concrete flaws. You can mix and pour them out on your concrete floor to remove depressions, dents and valleys. They will automatically flow to the depressions in the floor, where the epoxy will harden and leave behind a level concrete floor that you can install wood flooring on.
For burs and spikes in the concrete floor, use sanders or scrapers to help prepare the surface. For smaller ridges, a scraper can usually knock errant concrete down to size. For larger ridges, you may need to use a sander or similar tool to wear the surface area down. Keep in mind that this will also wear off the sealant -- but resealing the concrete slab before installation is a good idea anyway.
If patches of the concrete floor are beyond repair or the floor is too worn overall, consider replacing it entirely. Cracks and broken areas in a concrete floor will continue to cause problems even if you cover them up with floor boards, so it is better to swap these sections out for new concrete entirely. This also gives you the opportunity to add vapor barriers,