Most of this post is going to refer to unofficial clans.

Being a good leader takes a lot of things. Primarily, I'd say it takes activity, discipline and dedication.
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1. Activity - Look at, for example, many of the forum inactive clans in Clan Discussion. Most of the time, you'll see that the leader/founder isn't posting much. It's important to realise, especially when your clan is first starting out, that your clan is only going to be as active as you are. In most clans, people aren't going to keep posting on their own, so post yourself until they do. If they're not posting at all, poke them until they do. This also applies ingame - for example, if you're the only guy that can start Clan Wars and you're not active ingame, your members have suddenly just lost an incentive to go ingame, making your clan significantly less active, less appealing and less likely to develop and become official.
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2. Discipline - Speaking from personal experience, discipline is a great thing to have when it comes to clans. For example, recently I had a problematic member that was getting on everyone's nerves. For ages, I'd manage to dance around the topic and allow him to stay in the clan since he was a friend, to the dismay of my clanmates. He's recently been kicked and I can only wish that I'd used discipline earlier to just get rid of people or things that are creating problems. Also applies to getting members to be active, keep reminding them until they start posting on the forums, join your Discord or whatever it may be that they need to do. If they're constantly not pulling their weight, get rid of them.
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3. Dedication - For obvious reasons, you need to be dedicated to your clan. Activity's a huge part in this one, but also, don't give up. Prime example is [AS], they applied 3 or 4 times for official before they were accepted, and their leader was passionate about the clan and never gave up. Another example is (o) Originals, the leaders gave up after things took a turn for the worse and decided to kick everyone. No hard feelings to the leaders of that clan, but it (giving up) basically killed a clan that could have stayed alive, and was doing well. Someone posted above about not doing things without asking the clan, I think this shows what that can do to a clan.

I was.

I made [a] Adventure and got it to official. I'm not as active in the board as I used to be, so I'm not doing as good a job as leader as I was before.

One of the biggest mistakes people make is recruiting the wrong people. If you're recruiting people who just post "hey" or "i want to war", you're getting the wrong people. If your members are on the forums once a week, you've got the wrong people. Recruit those that you know are decent people, at least.