When designing commons for a set, there is a strict limit on what is considered accpetable complexity. This was outlined in Mark Rosewater’s article “New World Order”, and Reuben Covington did a stellar primer on how to design for NWO here.
The list below, pulled from Reuben’s primer, indicates every indicator that a card is red-flagged (not typical at common). The two rules of thumb to remember are that 1) Less than 20% of your commons overall should be red-flagged, and 2) Any red-flagged cards you keep in your set must make an important contribution to the set’s theme or limited environment. Each red flag has a linked example of how not to do it - for more information, check out the primer.