sql - Making a SQL query more efficient

Question

okay, so our server here at work isn't the best, and when I run this query it really throttles down everyone using anything on our server. Is there anyway I can make this query more efficient? I'd like to be able to run the query without everyone freaking out and say we are going slow the query basically outputs

Order Number | OrderDate | Sku | quantity | item price | our shipping $ | number indicating if it is paid | authorizeddate | amazonorderid | ebaybuyerid | Tax | TaxAmount | Shipping |Shipping Amt

The query returns everything I need, but I feel it could definitely be rewritten. I tried but it kept slowing down the server with queries that weren't working any help would be appreciated!

SELECT g.ordernumber, 
       g.orderdate, 
       p.sku, 
       p.quantity, 
       p.name, 
       p.unitprice, 
       s.shipmentcost AS OurPrice, 
       e.rollupeffectivecheckoutstatus, 
       ' '            AS wonder, 
       ' '            AS AmazonorderID, 
       e.ebaybuyerid, 
       f.type         AS TAX, 
       f.amount       AS TAXCHARGE, 
       x.type         AS SHIPPING, 
       x.amount       AS ShippingCharge 
FROM   [ShipWorks].[dbo].[orderitem] p, 
       [ShipWorks].[dbo].[order] g, 
       [Shipworks].[dbo].[shipment] s, 
       [Shipworks].[dbo].[ebayorder] e, 
       [ShipWorks].[dbo].[ordercharge] f, 
       [ShipWorks].[dbo].[ordercharge] x 
WHERE  g.orderid = s.orderid 
       AND f.orderid = g.orderid 
       AND x.orderid = g.orderid 
       AND g.orderid = p.orderid 
       AND e.orderid = g.orderid 
       AND f.type = 'TAX' 
       AND x.type = 'SHIPPING' 
       AND CONVERT(CHAR(10), orderdate, 120)BETWEEN 
           ( '2013-09-16' ) AND ( '2013-09-17' ) 
UNION 
SELECT t.ordernumber, 
       t.orderdate, 
       i.sku, 
       i.quantity, 
       i.name, 
       i.unitprice, 
       g.shipmentcost, 
       ' ' AS RollupEffectiveCheckoutStatus, 
       r.authorizeddate, 
       ' ' AS AmazonorderID, 
       ' ' AS EbayBuyerID, 
       f.type, 
       f.amount, 
       x.type, 
       x.amount 
FROM   [ShipWorks].[dbo].[order] t, 
       [ShipWorks].[dbo].[prostoresorder] r, 
       [ShipWorks].[dbo].[orderitem] i, 
       [ShipWorks].[dbo].[shipment] g, 
       [ShipWorks].[dbo].[ordercharge] f, 
       [ShipWorks].[dbo].[ordercharge] x 
WHERE  t.orderid = r.orderid 
       AND t.orderid = i.orderid 
       AND t.orderid = g.orderid 
       AND t.orderid = f.orderid 
       AND t.orderid = x.orderid 
       AND f.type = 'TAX' 
       AND x.type = 'SHIPPING' 
       AND CONVERT(CHAR(10), orderdate, 120)BETWEEN 
           ( '2013-09-16' ) AND ( '2013-09-17' ) 
UNION 
SELECT t.ordernumber, 
       t.orderdate, 
       i.sku, 
       i.quantity, 
       i.name, 
       i.unitprice, 
       q.shipmentcost, 
       ' ' AS RollupEffectiveCheckoutStatus, 
       ' ' AS AuthorizedDate, 
       a.amazonorderid, 
       ' ' AS EbayBuyerID, 
       f.type, 
       f.amount, 
       x.type, 
       x.amount 
FROM   [ShipWorks].[dbo].[order] t, 
       [ShipWorks].[dbo].[amazonorder] a, 
       [ShipWorks].[dbo].[orderitem] i, 
       [ShipWorks].[dbo].[shipment] q, 
       [ShipWorks].[dbo].[ordercharge] f, 
       [ShipWorks].[dbo].[ordercharge] x 
WHERE  t.orderid = a.orderid 
       AND t.orderid = f.orderid 
       AND t.orderid = x.orderid 
       AND t.orderid = i.orderid 
       AND t.orderid = q.orderid 
       AND f.type = 'TAX' 
       AND x.type = 'SHIPPING' 
       AND CONVERT(CHAR(10), orderdate, 120)BETWEEN 
           ( '2013-09-16' ) AND ( '2013-09-17' ) `