Bats are nature's best mosquito eaters and should be welcome in any yard. To attract them, Bird Man Mel suggests that you buy bat houses with multiple chambers and mount them in a high area facing the early morning sun. Don't fret if you don't see bats right away - it can take 6 months to a year to attract bats to your new bat house.
Video - Bird Man Mel's Attracting Bats
great video with instructions on how to attract nighttime bats to your yard