What to look for...
Make sure you tick all the right boxes on your macro lens wish list
Lenses with a longer focal length have a greater minimum focus distance, which is generally more convenient for macro photography.
Autofocus is great for general shooting but, due to minuscule depths of field involved, precise manual focusing can often work better for macro shots.
With an internally focusing lens, the front element doesn’t physically extend at shorter focus settings, which can be an advantage when shooting extreme close-ups.
This is nice to have but its effectiveness will be much reduced at around 0.5x magnification and of little value at all at full 1.0x magnification.
FX lenses are generally fully compatible with DX-format bodies, but you can only use DX-format lenses on an FX body in ‘crop mode’.
The fairly fast f/2.8 aperture rating of most macro lenses is a bonus for general shooting but the use of very narrow apertures is often necessary for extreme close-ups.