Remember Where You Are
First, you need to go over in your mind where your last session ended. Were there dangling threads that needed to be tied up? If so, good, your first order of business is going to be getting those tied up so work on that first. If not, not bad, but it means you need to figure out where you're starting. Putting some time between last session and this session ICly can help because it gives everyone the feeling time has passed and means that everyone is trying to figure out where there characters are. It's not always viable though, especially if the PCs were in the middle of potentially time sensitive events (like a festival, or with the world ending on the next new moon.)
Side Quests Can Be Great
Don't have a bunch of threads to tie up, and not blowing up the world come Tuesday? A side quest might be the answer for you. A side quest lets you progress things, and add depth to something, without necessarily touching your meta plot. I suggest this because it gives you more freedom both on what to do, and in how you do it. TV shows, video games, and everything else are great at showing how to inject side quests too - up to just slamming one in front of the protagonists - so you should have some idea of how it works.
One Things Per Player
I like to have more, but when on short notice I go for one thing er player. That works out to one plot movement point per player in the game. It could be as short as a five minute scene, or something that spirals into more with the player's involvement, but either way I have something for each player at the table to give them some personal movement. For example, in my next L5R game
- One character will be approached by several suitors
- One character is going to have an old flame re-appear on their screen
- One character is going to be summoned to the castle
- One character is going to be approached by a new friend
- One character is going to be told how out of their league they are
- One character is going to have tea with their boss/superior
Those are all small things, but they can become larger things. More to the point, that gives each player some progress on their personal front, which also gives them stuff to discuss with other characters and make plans around.
My notes have more detail for each one - but being vague as my players read this - but even just those one line notes are enough to work with. They're also vague enough I could pull them from a hat at random for any character rather than go with the ones intended.
Combat Eats Time
Working in combat - if you can do so in a meaningful way - is another way to eat up time. I don't recommend just throwing a fight at the players in the hopes of killing half the session, but if a fight is coming up - or is plausible - making it a bit bigger (don't forget to amplify reward as well) can be a good way to not just eat up time, but fill the game session with content.