Difficult to hint what the tuning should be without seeing the “registration” information (detailed view) and its fluctuation over time. That, together with “freq usage” and “snooper” scans, would give some clue on what is causing your poor wifi experience.
Remedies are like moving the AP away from wall and furniture. Check signal strength in both directions. Avoid interference by moving channel and even by lowering bandwidth.
Sending smaller aggregation packages can avoid large retransmits (but this also lowers the max data throughput) , by reducing the A-PSMDU from 8192 to 2048.
Improving the respons time on time and jitter critical communication, by setting the user priority and enabling WMM. (enabling WMM without setting priority doesn’t help much)
http://forum.mikrotik.com/t/how-to-get-rid-of-slow-wifi-can-it-be-done/139640/1
If you start using user priority don’t forget to extend the use of A-PMDU for those other priorities except voice (7)