So how do you be good at this bidding thing?

You don't. This event (like most recent Steam events) is made for rich people.

You don't. Only the top payer can win.

Think really hard about winning and then go to sleep.

There are a ton of games out there with a top bid around 5000 gems, but more importantly still with less than 100 bids in total. There definitely is a chance to win a game here with 1000 or less gems.