I bowled left arm spin, here's my defensive field setting:-
5 offside - slip, backpoint/point, deep cover,extra cover, long off
4 legside - 45 on the 1, deep square, midwicket, long on
More attacking would be to bring long off/on in and deep extra. If it's turning big then move backward point to gully, then either move cover to point and/or extra to short extra. Could also bring deep square across.
Pace of the deck and outfield also important, as well as the pace you bowl. Slow deck/pace - point more important, quicker deck or quicker through the air then backward point.
Job done. Bowling figures in the league - 26.1-8-36-5