So I made this guide a while back, hopefully y'all can learn a thing or 2 from it
Step 1: Stalk your item. Check the boards, auction genie some common mispriced items (Paint Brushes, Draik/Krawk Transmogrification Potions, stuff newbies get for free)
Step 2: WAIT! Don't go placing a bid with 2 hours left to go, all you will do is drive the price up and incite panic, and let more people notice that this item is hot.
Step 3: Once your item hits <30 mins left, keep checking the 21-40 auction page. Refresh often enough that it never slips from 61 to <20 without you looking, but you don't need to refresh every half second
Aside: Another way to find out approximately when an item will be done is to look at the first bid. Usually first bids happen pretty quickly on popular items (Draik TP, Mootix, ect), so theauction will end on that minute, or a few minutes before. So if the first bid is at 8:12, the auction will probably end on 9:10-12, 10:10-12, 11:10-12, ect. If it's at <30 mins at 12:00, it'll probably end at 12:10-12.
Step 4: When the item reaches the 21-40 auction page, pick an amount 10-20k above the current bid (depending on how fast bids are going through, and click "Bid". On the next page, if it says "you cannot bid more than 5k over...", then simply refresh that page (press enter to accept the box) over and over, until the bid goes through.
Step 5: Once the bid goes through, immediately press the back button on your browser, increase your bid by another 10-20k, and repeat step 4. You won't win every auction, but you'll find yourself winning a lot of big ticket auctions that you never thought you'd have a shot at.