An obvious tip but a time-saving one. Decide what to buy so you can save a lot of time by zeroing in on the best offer for that product instead of just aimlessly scrolling around different categories for deals. Once you have decided what to buy, you can check various price comparison websites or even browser extensions that let you compare prices of items across major shopping portals. Some also mention details of any additional offers from banks/merchants which can help to save money when shopping online.
Coming to tie-ups, most shopping sites have partnerships with one or more banks during major online sales. In addition to these, there are dedicated coupon sites which share some of their affiliate commission with you if the purchase is made via their website or referral link.