Common mistake is to go shallow when the answer is often to go deeper. Also reduces tool wear because cutting too shallow is most common cause of excess tool wear.
However small cutters are slightly more difficult to deal with because of there tendancy to want to snap for no ryhm or reason.?

Rule of thumb for run of mill sizes ie 4mm up is DOC 50% diameter. Below 4mm then drop to 30% or lower for really tiny cutters.

Obvioulsy cutter type and coating ie Carbide Ti etc will be very differant to HSS so you'll need to adjust accordingly. Carbide tooling is more expensive but often worth the expense because you can cut deeper and faster and with less tool wear. It's not uncommon to cut 100-150% dia with carbide tooling in some materials.

So many factors come into play but don't be afraid to cut deeper you will get a shock just how deep you can cut with some tools and materials. It's worth sacrificing a few tools/materials to find the limit or best setup because if doing lots of the same material it will save you time and money in tool wear.