When applications open, homebuyers will apply on the HDB website for the property and unit size they want (e.g. Toa Payoh, 4-bedroom).
Then, after the applications are closed, HDB will use a computerized voting system to assign queue numbers. Usually, after three weeks, the voting results will be announced.
The queue number is the order in which applicants will be given their selected flats. This means that if your queue number is within the range of flat availability (for example, there are 124 flats to choose from and your queue number is 124 and below), then you are likely to get a flat.
If your queue number is higher than the supply of flats (for example, there are 124 flats available and your queue number is 125 and above), then you will only get the chance to pick a flat if the person in front of you in the queue decides to give up the chance.
HDB has some priority schemes to help increase your chances of getting a queue number. However, queue numbers are randomly assigned so there is no way to somehow get a better queue number.
This means that while you can double your chances of getting a queue number, you can't do anything to get ahead in the queue and pick first.
By default, if you are a first-time lottery entrant, you get twice as many chances to vote as a second-time lottery entrant. Keep this in mind when you make your first application so you don't waste your chances.
To help those who have had multiple unsuccessful attempts, don't lose hope! If you are unsuccessful in two or more attempts (at a non-established property), you will be given an extra chance on a subsequent application.
The "racial quota" that most people know is the Ethnic Integration Policy (EIP), which was introduced in 1989 to encourage racial integration.
Basically, for each HDB district or neighborhood, there is a limit on the total percentage of housing that can be occupied by a particular race.
While this is not something you can do, it affects your BTO chances because the actual number of units you are eligible for depends on it.
Let's say you get queue number 100 and the total supply of units is 124 units. If the racial quota is reached before your turn comes, you may not get units.
For example, if you are Chinese and the 90 units allocated to Chinese families have all been snapped up, you don't stand a chance.
In this case, your application will be voided and you will not be penalized for refusing a BTO unit.