This is very tough without knowing your config...some things that will make a difference (or not) depending on what the issue is
1. ARM features - band steering, spectrum load balancing, fair access
2. If you can upgrade, do it for ClientMatch
3. DEFINITELY enable broadcast filter all on the VAP profile. Like the former comment mentioned - so long as there isn't a multicast video. This CONVERTS broadcasts to unicast to the WLAN client. Very useful to combat ARPs, DHCP, etc...from consuming precious throughput.
4. Turn off the low data rates in the SSID profile
4. Increase the local probe response threshold to 20 or 25 in SSID profile (advanced tab)
5. Enable deny broadcast probe (see above)
6. Enable BC/MC rate optimization (in SSID profile advanced tab)
7. Enable fair access by creating a traffic shaping QoS profile. Apply it to the AP Group