New DMs post your questions here! Experienced DMs try and answer them!

For all those new DMs out there!

You can bet I struggled as a first-time DM, and I was hoping that I could ease some of that trouble off others <3.

THERE ARE NO STUPID QUESTIONS.
If you think there are, I'm siccing my treant on you

I may not be a fully new DM, but I still have a few questions. The main one is how I can keep my party engaged during combat.

I've been trying to teach some of my friends how to play, but that results in really slow combat. How do I keep people engaged?

I am not sure this thread is necessary - folks are capable of posting individual threads to ask questions, and those individual threads have a history of getting individualized responses.  Compilation threads like this run the risk of any individual question going unanswered, as there is not an individual thread drawing attention to an individual’s present needs.

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While I think the thread itself is counterproductive and detrimental, I do want to take the time to answer your specific question. 

Combat is notoriously the slowest part of D&D and the hardest to keep players engaged during.  By virtue of being formulaic with set delays between individual action, it is easy to get distracted or bored during others’ turns.

Typically, I find the best way to keep folks engaged in combat is to make paying attention important.  Enemies should be intelligently moving, so people have to reassess the situation.  Damage amounts should be significant to add tension and force players to reevaluate their resource allocation and future action economy. There should be additional environmental things going on that players have to track.  And, of course, being ready when it is a monster’s turn so you do not spend time equivocating and slowing down combat. 

Basically anything to keep the fight a dynamic affair instead of a tank and spank.

Some of these problems also shake themselves out as players get more experience.  The most boring part of combat is watching a player struggle to figure out what to do on their turn, and that is a bit of an inevitability when dealing with newer players.  As players get more experience, their turns tend to move a bit quicker, mitigating some of this delay.  This is something you as a DM cannot really fix, other than by being patient and trying to help them learn to move faster. 

Some DMs put a timer on players’ turns to force combat to move faster, so that is something you can also consider if you think it would be beneficial and accepted by your group.  That has some of its own pratfalls, including potentially making players feel upset or frustrated, so it is not for every group.

For your combat question, I would suggest making the terrain dynamic and making every combat relevant to the plot. Add obstacles and cover, maybe some random tables when relevant. And don't just throw around random combats that don't do anything for your story. Make them all mean something, whether it is to set atmosphere or advance the story in some way. Personally, I've stopped using random encounters and only put in things that contribute somehow to the story, unless random encounters were specifically necessary (exploration scenarios, small localized encounters with guards, etc.) It's a choice, and I'm sure many people would fight me on this, and I'm sure there's a way to use random encounters in a way that fits my purposes, but I've found it helps me.