The two best ways I've used large creatures is either having them as multiple "parts", allowing the players to disable the different body parts of the creature. For example, cutting off a Kraken's arm to reduce the number of chances it has to attack and grab the party.
The other way is to feature them as terrain elements of other encounters. Maybe the party must fight there way through an enemy army to escort their NPC friends out of a city while a dragon flies over head, with the dragons breath weapon/debris it knocks aside with it's swinging tail, wind made by it's flapping wings, etc affecting the fight.
In general if you're running huge creatures with massive damage abilities - telegraph attacks. Have the dragon's maw fill with fire a turn before you use the breath weapon, etc. If players feel like they can anticipate what is going to happen getting hit out of nowhere will feel less like an anticlimax.