In this game, everyone seems to be in different clans, and advertising different things. For the casual player, they can join pretty much any clan and be happy in it. But for players looking to move up the ranks, there are not as many clans that will really help you along. I personally had much trouble finding a good clan when I was a new player, and when I got higher ranked. This guide is to show the aspects of a good clan to see progression in yourself.
The first thing you see about a clan as a whole is the clan page. The description, clan trophies, players and their levels, players' trophies, and now players' donations are all visible. You can also easily see the elders in the clan. If a clan has few members, and does not state that it "feeds" into another clan, it was likely thrown together hastily without much planning. These clans are generally good for casual players. Also, if a clan has a high number of players, but low trophy points, check the players levels. If they are all low level players, this is likely a group of new players wanting to belong. If they are higher levels though, you may have stumbled upon a farming clan. Based on what you want from the game, this might be a good fit.
The next thing you can check is elder status in a clan. The two extremes are no elders, or everyone is elder. In a clan where only there is only a leader, this may be a sign the leader made the clan, and then stopped playing the game or has been inactive. These clans can get unruly without effective leadership, so avoid at all costs. Similarly, a clan with all elders is also a warning sign. If everyone is elder, only the leader can kick members out. Also, the clan members feel like elder is worth having, but in reality, there is no value to holding the title if everyone has it. Again, avoid at all costs if you want to grow. When eldership is earned in clans, it shows loyalty among the members and elders, this is great to look for. Elders are to be given to players who help out a lot, and who look out for the clan as much as possible.
This may be self-explanatory, but I will cover it anyway. Clans with curse words indicate a less mature clan. Proceed with caution. Clans named after any of the top ranked clans are people trying to trick people into joining. These clans generally have no real goals, stay away. Clans with names based on popular culture can be based primarily on a common interest. Depending on what you want in a clan, judge according to your own tastes. Misspelled clans are either hastily thrown together, or made to be humourous. The former is a warning sign, the latter indicates a fun clan. This is a game, so there is nothing wrong with joining a clan for the fun aspect.
The way a clan describes themselves is a great way to see how a clan is organized. If a clan description is missing, it shows a lack of leadership, and no clear clan goals. This is a warning sign, but not a clear indication to stay away. A clan could just be updating the description. If there is no description within 15 minutes, that is a better indication to stay away. If the description has many spelling mistakes, this is a caution sign. Bad spelling isn't always a bad sign, some people simply can't spell right. If a clan has clear, concise rules in the description, this shows a very good organization and goals within the clan. This is something to look for ideally.
There are two things to watch out for here: how much the clan donates and how much you can donate. If the clan doesn't donate much, they are either inactive or selfish players. If a clan has over 1000 donations per player, ask yourself "Can I donate as much as they do?". If not, the clan may not tolerate a lack of donations from you. Find a clan that donates roughly as much as you think you can or have donated in the past. Remember, donations cost elixir, 1000 donations can easily cost over 100,000 elixir. Think about what you can afford.
Find out what a clan donates by default, if it is not listed in the description. Most clans I've experienced prefer archers, as they are versatile for attack and defence. If the clan has a default that you like, and that you can give back regularly, then it is a good fit. Also, see what the clan is willing to offer. Don't join a clan that doesn't have wizards if you have dragons and people ask for them, it drains your elixir. Find a clan that has similar troops to you, and roughly the same level if possible. Players with max level troops don't like level 2 troops in return most often.
This plays a bigger role than you would think. If a clan is active, then they are generally structured well. Also, they can usually joke around easier, creating a sense of family within the clan. Clans that can talk a lot can generally drop some advice while casually talking, and are more inclined to answer your questions than a clan that doesn't talk much.
Clans that have more than one clan headed under the same name or mutual leader are generally very loyal. They have gathered enough people who are like-minded and share the value of growing a great top clan while working to improve themselves in the best way possible. Not to say that single clans are bad, but clan families generally contain most of the good aspects of a clan throughout all the clans they have
In conclusion, there are good clans out there. I myself have been fortunate enough to find an amazing clan family, but I had to look long and hard. Pay attention to what people recruiting in the global chat have to say, you can learn a lot based off of their words. A great clan produces great players.