Create Procedure NewOrder
       @customerid NUMERIC(9),
    @total    FLOAT ,
    @discountamount FLOAT,
    @discountpercent FLOAT,
    @Remarks VARCHAR(MAX),
    @StatusOrder NCHAR(10),
    @DateCreated datetime,
    @datemodified datetime,
    @CreatedBy    numeric(9),
    @ModifiedBy numeric(9),
    @IsActive bit,
    @DomainName nvarchar(300),
    @Years int,
    @BillToID numeric(9),
    @BillType numeric(9),
    @domaintype nvarchar(300),
    @totaloriginal float,
    @serialnum VARCHAR(MAX),
    @productid numeric(9),
    @quantity int,
    @totalprice float,
    @billingID numeric(9),
    @promotionID numeric(9),
    @promotionTypeID numeric(9),
    @unitprice float 
AS
BEGIN

    DECLARE            @counter int
    DECLARE            @ordernum numeric(9)
    DECLARE            @orderprefix nvarchar(300)
    DECLARE            @maxorderid NUMERIC(9)


    SELECT @counter =Count(*) FROM TBL_Order    

    IF (@counter = 0)
    BEGIN
            SET @ordernum ='1000'
    END
    ELSE
    BEGIN
            SELECT @ordernum=MAX(ordernumber) FROM TBL_Order
            SET  @ordernum =@ordernum +1
            /*SET @newordernum = @orderprefix + ' ' + @newordernum*/
    END

    IF (@ordernum IS NOT NULL)    
    BEGIN 

            INSERT INTO tbl_order(Ordernumber,OrderPrefix,CustomerMasterID,TotalAmount,DiscountAmount,DiscountPercentage,Remarks,StatusOrder,DateCreated,DateModified,CreatedBy,ModifiedBy,IsActive,DomainName,Years,BillToID,BillType,domaintype,TotalOriginal,SerialNum)
            VALUES(@ordernum,@orderprefix,@customerid,@total ,@discountamount,@discountpercent,@Remarks,@StatusOrder,@DateCreated,@datemodified, @CreatedBy,@ModifiedBy, @IsActive,@DomainName,@Years, @BillToID,@BillType,@domaintype,@totaloriginal, @serialnum)
            IF @@ERROR <>0
                BEGIN
                    PRINT 'ERROR OCCURED'
                END

            SELECT @maxorderid = @@identity  

            INSERT INTO tbl_details(OrderMasterID,ProductMasterID,Quantity,Total,BillingCycleID,PromotionMasterID,PromotionTypeID,DateCreated,DateModified,CreatedBy,ModifiedBy,IsActive,UnitPrice)
            VALUES(@maxorderid,@ProductID,@quantity,@totalprice,@billingID,@promotionID,@promotionTypeID,@DateCreated,@DateModified,@CreatedBy,@ModifiedBy,@Isactive,@unitprice)
            IF @@ERROR <>0
                BEGIN
                    PRINT 'ERROR OCCURED'
                END
    END
END

Also you should write one stored procedure for each table. 
do not write everthing in one procedure. 
Error message will come to your front end code directly. 
Print command will not help it will show message only if you execute query in query analyser.