Copy from a monero dev answer on reddit: Heuristic I not applicable to RingCT, so moving on... Heuristic II is basically people sending a transaction to thems

Copy from a monero dev answer on reddit: Heuristic I not applicable to RingCT, so moving on... Heuristic II is basically people sending a transaction to themselves and thus creating 2 new txo's (amount and change). Then at some point people spend both txo's in one transaction. This is something that can be avoided by just not sending coins to yourself and by the wallet giving you a warning when you are about to spend 2 txo's stemming from the same txo. Heuristic III is basically the fact that the newest txo in a transaction is likely the one that is being spent and can be prevented by people actually keeping a small reserve of XMR and refilling this at random intervals. Don't spend all your XMR all at once just after you received it.