You will no doubt have heard the terms "big stack" and "short stack" in your poker career regardless of how experienced you are. These two common poker terms refer to how many chips a particular player has at their disposal. The reason the word stack is in there is because players stack their chips up in towers in front of them, but how they stack them can give an indication to how they are feeling, their experience level and if they want to gamble.
When you are transporting your chips from the cashier's cage to your table or from one table to another, you may use a plastic chip rack to aid you. These racks can hold 20 chips in each slot, so guess what the industry standard is for stacking chips in? You guessed it, stacks of 20. If you see a player stacking their chips in towers of 20 then you can assume they have a decent amount of experience playing live poker.
You should also pay attention to how neatly an opponent stacks their chips, regardless of how many chips are in each stack. If a player is meticulous in their arrangement of their chips and makes them extremely neat, sometimes even with the patterns aligned perfectly, then they are likely to have the same approach to their game. Their hand selection will be carefully decided and they are not as likely to have huge amounts of gamble in them.
The complete opposite of Mr Neat Stacks is the player who seems to not care about how his chips are arranged. There may be a stack of 20 that resembles the Leaning Tower of Pisa, and it may be surrounded by a few loose chips, a stack of 12 and another of 17. Their careless stacking of chips can often be an indicator of a careless playing style too.
A time when everyone's chips are in a mess is shortly after winning a substantial pot and having the pot pushed towards them, which results in chips scattered everywhere. The majority of players prefer to stack their chips before they get involved in a hand, but this does not mean they will fold strong holdings. Many players like play the next hand they are dealt after winning a hand - Doyle Brunson says in his book Super System that he used to do this do to winning streaks - but they will rarely run a bluff from scratch when they have chips scattered in front of them. Indeed, they may turn their hand into a bluff after the flop, but their initial holding will usually be at least semi-decent to start with.