Well if both animals are avoiding each other and going on one end of the enclosure you will know that they have no interest.
You may observe
tail wagging
blood smear int the enclosure if you use paper
Finding the male on the top of the female
Now what is important to remember is that your animals will often be more receptive during cool front, low pressure, storms etc. It is also important to remember that the first couple of pairing don't always lead to copulation, however as the female will start developing follicles (which is important to watch for that) it will be more important than ever to introduce the male at that time and copulation will more than likely occur.
Now sometimes even with the right conditions and a female starting to build follicles the male might still not show interest, in that case there are a few tricks that may help.
The whole thing is really something you pick up little by little spending time studying YOUR animals, and usually the first year most people have no clue (I didn't) and pair often and up until ovy just to make sure.