zip ties, zip ties, zip ties…did I mention zip ties? Most road bikes have very little clearance so mounting fenders can be a pain.
The bolt kits that come with most fenders are useless in my mind. They often never work on my bikes. Start off by pre-mounting, positioning the fenders on your bike with the ties, then adjust as needed with other ties. Home made mud flaps are a necessity as standard full fenders without them don't offer enough protection for you and your drive train.
I also use pieces of old tubes to wrap around the frame before I zip tie the fender rods. This will protect the frame from metal on metal rubs and cut down on the creaks and rattles that fenders tend to make.