PLO bet sizing
An effective way to know what to bet in different hands of PLO is to study the tables you are sitting at.
When you first sit down at a table things you should look for are the overly aggressive players. Every player that plays PLO is known to be aggressive, but the overly aggressive are the ones that you can pick off in a big pot.
How to bet against a player that is overly aggressive is either to check, and let them hang their self or to make relatively small bets compared to the size of the pot (25-40% of the pot).
What you want to avoid is leading out and betting pot when you are sitting with the nuts on a rainbow board. You will get no value for your hands if you do that. Ideally, you would like them to bet pot and you can come back over the top with a superior hand or you can just call and let them continue betting.
Bet size depends on position
The size of the bets you make should also be compared to the position you have at the table.
If you are playing in a shorthanded game with 6 or less players then you should almost always put in a raise that is 2.5 the blinds ranging up to a pot bet before the flop. This opening raise is dependent on first how strong your hand is, and second where you are at the table.
If you are in early position and your hand is strong enough to play then you should be opening for a pot sized raise. If you are in later position and just trying to pick up the blinds with a weaker hand then your raise should be to 2.5 times the blind.
If you can demonstrate pot control before the flop then you can control the action and the betting after the flop.
Betting for information
When playing the flop in a PLO game you should always see and try to figure out what your opponent has, so, you should almost always bet. How much to bet depends on how hard you have hit the flop.
If you make the nuts, something such as a set or a straight on a draw heavy board you should always bet whether you are in position or out of position. If you check out of position and your opponent checks behind you a scare card can come out and cause you to lose the hand. You should be betting around 60-70% of the pot if you have it.
The only time to utilize a pot bet would be with wrap type of draws or if you know someone is unable to fold and you have them beat. If you have a hand that is not there yet, but can improve to be there in a number of different ways, such as making a straight and a flush, you can make the pot bet.
If you get called or raised back in spots on a hand where you have 15 outs to make a straight or a flush this is a profitable play for you. The reason it is profitable is because some of the time they may raise you with a worse hand than yours and other times they might even just throw their hand away.