I've already given my best piece of advice, but here's my second. At least, it's second for me considering how I DM.
Plan for the next session at the end of the current session. Oftentimes someone has to be home at a certain time, the gaming store is closing, everyone is mentally drained/too excited by killing the BBEG to do this.
But take the time to plan the next session. Where will you play? Who can make it? What time? And then do in-game planning. Will the players travel somewhere? Are they going further into the dungeon? Are they up for following up some side quest? A few minutes at the end of the current session go a long to make the next session better.
But likewise, don't be afriad to say "NO" when you need to. There are plenty of good reasons to say no, not just to in-game activity but player behaviour, attitudes and actions. Not everything that happens at the table is okay. Nor should it be. A DM must have a firm and steady hand and be willing to use it.
And that plays into my advice: Be firm. Make a decision and stick to it. Maybe it's the right decision, maybe it's the wrong decision. Waffling over it will not benefit you, your players, or your game. Be consistent.