Using If Statments In A Stored Proc

i'm passing 4 paramaters to a stored proc. based on the values of the paramaters i add conditions to my select. can som one please reviwe the proc below and tell me if my syntax is wrong or if there is another way of doing this.

Thank You,
Thomas


CREATE PROCEDURE [Multi_Picking_Slip_FillListview1]
@str_Division nvarchar(50), @str_Season nvarchar(50), @str_Cust nvarchar(50), @str_ShipTo nvarchar(50) AS

SELECT * from tblDistribution WHERE PikingNo = 'NO'

If @str_Division <> ''
AND Division =@str_Division

If @str_Season <> ''
AND Season = @str_Season

If @str_Cust <> ''
AND cusNumber = @str_Cust

If @str_ShipTo <> ''
AND shpStoreNo = @str_ShipTo

GO