*Make sure that your player heir is also your primary heir. Take note of your realm's succession laws and any active elections, and change them if necessary. Ensure that your heir gets the lion's share of your inheritance by selecting the most favorable succession laws available.
*Prevent your realm from fragmenting upon succession if you have both multiple heirs and multiple titles of your highest rank (if above count-equivalent) by creating a higher-tier title or destroying extra titles that are equivalent to your highest rank title.
*Characters' opinions of your character modify their opinions of your heir upon succession. Dread is useful while your character is alive, but is not inherited by your heir. Either make amends with your domestic enemies or neutralize them when your character becomes old, has health penalties or you suspect that murder plots are underway against your character.
*Don't panic if your realm fragments or powerful factions are created against your character upon succession. You will get claims to any titles that you lose. Plot to take your former realm, even if it takes more than a generation to do so. Remember that unpressed claims are only inherited by your children if you fight a war for those claims while your character is alive.