Answer me some questions, yeah?

I'm very much an improviser. Which is to say, I don't plan much in advance. Sometimes plans develop over the course of an adventure, but I don't have them at the start.

I suppose the main advice I have is, don't worry too much about the details of the plot. If you have big scenes in mind, you can direct people towards them when you need to. If you need to build up to those scenes, well, just make sure to include some of that buildup no matter what happens.

Really, you only have two goals.
-Keep it interesting.
-Don't let the scope get so big that you can't handle it.

Any tips I could give on the first would just boil down to "be a good storyteller". You can find that advice in plenty of places, so I'll focus on the second.

If you have a general plot in mind, stay on it. Don't deviate. I don't mean you have to railroad, just make sure all your paths have the same destination. If you find the path is going in a strange direction, tie it into the main plot somehow.

Most importantly, remember that your protagonist isn't the only force in the adventure. Antagonists or other powerful parties can push their way into any plotline at your discretion. If you feel like the plot's getting lost, then drag it to where the story currently is.

Finally, communication is important. If the tone of suggestions is way off from what you want, say so. (Politely, of course.) The people here will be happy to adjust if you just ask.