Add the options which have been provided so far won't use your indexes at all.
Something like this will do the trick, and make use of an index on the table (if one exists).
DECLARE @StartDate DATETIME, @EndDate DATETIME
SET @StartDate = dateadd(mm, -1, getdate())
SET @StartDate = dateadd(dd, datepart(dd, getdate())*-1, @StartDate)
SET @EndDate = dateadd(mm, 1, @StartDate)
SELECT *
FROM Member
WHERE date_created BETWEEN @StartDate AND @EndDate