Unless you're a dedicated outliner - and even then! - you may find yourself asking "Now what?" during the drafting phase as you reach the end of your wits...I mean, your planned scenes! If that's you, then this post is here to help!
Listen to Music! Music is a FANTASTIC way for many writers to plan ahead! Plug in your headphones or crank it up on your speakers and try to envision the next scene, or even many scenes in the future. Sometimes just anticipating some moments down the line will help you figure out what needs to happen between here and there.
Read in Your Genre Struggling to figure out the next step in your cozy mystery? Unsure what trial should obstruct your fantast adventure heroes? What CAN you do to make life harder for your sci-fi heroes in their high-tech space station? Sometimes ideas lie within your genre as a whole! Of course, I'm not advocating ripping something straight from another book; however, the more you immerse yourself in the feel and style of your genre, the more likely you are to think in terms of that sort of worldbuilding and structure - which can help you figure out the next steps to take in YOUR world!
Make Time to Brainstorm Figuring out what to do next is undeniably tough if you don't make time to - well, figure out what comes next! If you're struggling to think it through, carve out some dedicated time to do nothing but focus on what comes next in the story. Put your phone on airplane mode, release all your distractions, and brainstorm away!
Stay in the Scene Sometimes we writers get TOO much in our own heads! We may be writing one scene but worrying about the next six, or one way down the line! In these cases, it's wise to narrow your focus down. Just concentrate on figuring out the current scene and what comes next; don't try to think too far ahead!
Use Gaps Sometimes we just need space from our project to figure it out. Don't be afraid to step away for a long, relaxing weekend doing absolutely nothing related to the story. You may find the creative juices flowing much more freely with a bit of separation from your project!
Employ an Outlining Method. If needs be, try some (more) outlining! Methods like Save the Cat Writes a Novel, the Snowflake Method, and many others help writers get unstuck (or avoid ever being stuck at all!) by laying out some guidelines for what a successful plot needs in order to keep a reader engaged. Figuring out where your plot is a roughly where it could go next may help pull your mental wheels out of the mud!
IA note on #4: this was where I found myself when drafting a story lovingly titled PROJECT CAT AND MOUSE; day after day, I only knew what was going to happen in that day's scene, and that was IT! If you're worried that this style of writing where you only know the next step, one foot in front of the other, is somehow wrong...don't be! This is just one more beautiful method of producing your draft. Here's a quote I absolutely love, which I hope will encourage you on the way: "Writing is like driving at night in the fog. You can only see as far as your headlights, but you can make the whole trip that way."