Random opponent play: natural bids.
FRNat?: ask explicitly. Otherwise:

Openers: 1NT15-17, 2NT20+; HCP12+: 1h/1s = 5M, 1c/1d = no 5M, weak NT; 2h/2s = 6+ weak; 3c/3d/3NT = long strong minor.

Responses: Dbl1-2 = no opp suit, have HCP; suit lvlup = fit, no forcing. suit-to-NT = no suit; 1suit-to-2NT: no suit, have HCP14+