I had to answer this on the fly recently.
You may remember I introduced my new group by dropping them into a swamp where they met Druht, a depressed mud mephit. Druht disappeared when a horde of lizardfolk surrounded them and took them capture, and then held them in a hut at the back of their cave while talking about the great meal they were going to be part of.
They talked their way out by doing a deal with the shaman that they would try to persuade the local landowner to cede the marshes to the lizardfolk.
I realised they were thinking “yes, we’ll agree to this…but once we’re out, how will they be able to hold us to anything” so I had to think quickly how their actions could have consequences for thier characters.
So now their fighter is wandering around with a bracelet on his arm which has been magically put in place by the shaman and cannot be taken off, and which pulses every day in the middle of the day as a reminder of their promise. They have no idea what other powers it may or may not have, but there is clearly something there…
So – to make the stakes important, make sure the players feel their characters are actually threatened.
Next: how can we get more people playing?