3C = natural, 15-17, min 6 clubs (NF)
1H/S = natural, 12-17. might be balanced outside 1NT zone or clubs+M. might be 3 cards (with balanced hands, since 1C-1D-1NT is 18-20)
1NT = 18-20 balanced OR flexible (UNBALANCED) 18-21. (then, 2C=0-5, 2D=6-9)
2C = art GF (25+ HCP if balanced). (then, 2D=0-5 hcp, 2H=6-9 hcp with 0-1 controls, 2H=6-9 hcp with 2-3 controls, 2NT=2 aces)
2H/S = acol style, but NF. 1-suiter, 18-21. (then next higher step is negative, and a single raise is forcing)
2D = balanced 21-22 OR minor 1 suiter 18-22 (opener will bid 3C or 3D next) or GF minor 2-suiter (opener will bid a major fragment next). then, 2H=0-5 hcp, 2S=6-9 hcp.
2NT = balanced 23-24