Make sure that other potentially interfering devices are clear of the area (wireless phones @ 2.4G seem to be the main culprit).
Keeping the antennas clear of obstruction is another "big deal;" especially water bearing organic objects (like plants, trees, humans ...).
Generally speaking, altitude is your friend ... get the antennas as high as possible. Ceiling mount is a great way to go if you can swing it.
If you are talking predominantly to laptops, try the antennas in a horizontal configuration: most laptop antennas are horizontally polorized.
If your antennas are separated from the radio unit, try a lower-loss cabling and/or try some antennas with more gain.
You may want to verify that the radio unit is configured for max power.
Good Luck
Scott
