Find First Sunday of a month

There are several ways to find First Sunday of a month. The following is one of the ways

DECLARE @dtDate DATETIME
SET @dtDate = GETDATE() -- Replace with any other date
SELECT DATEADD(WEEKDAY,(8-(DATEPART(WEEKDAY,DATEADD(mm,DATEDIFF(m,0,@dtDate),0))))%7,DATEADD(mm,DATEDIFF(m,0,@dtDate),0))

First look at
DATEDIFF(m,0,@dtDate). 0 in datetime corresponds to 1900-01-01. We calculate the difference of months from 1900-01-01 to a given date. Once we get this we add the difference we got to the anchordate.
DATEADD(mm,DATEDIFF(m,0,@dtDate),0). This gives the firstday of the given month. Once we have firstday of a given month, we have to find the weekday of the day. In SQL server Sunday starts with 1 and Saturday ends with 7.
DATEPART(WEEKDAY,DATEADD(mm,DATEDIFF(m,0,@dtDate),0)). This gives a number from 1-7. Now we subtract the obtained number from 8 since, chronologically second sunday would be 8. Once we subtract from 8, we are getting the remainder of the value after dividing it by 7 as there are seven days in a week. This step is required because if first day of the month is first sunday, if we don't do a modulo, the logic will show second sunday as first sunday.
Once we have this value, we add this value to the weekday and the final query will be

SELECT DATEADD(WEEKDAY,(8-(DATEPART(WEEKDAY,DATEADD(mm,DATEDIFF(m,0,@dtDate),0)))),DATEADD(mm,DATEDIFF(m,0,@dtDate),0))

If you want to get first monday replace 8 with 9 and for first tueday replace 8 with 10...for first saturday...If you want to get second sunday add +7 to the above query for third sunday add +14 and so on....its that simple