Finding good players may seem like a 'hit & miss' but there are key indicators to improve the odds of getting a 'hit'.
The following are things to look for. It doesn't mean that you don't get the occasional hopper but at least they will be a good hopper :)
1) Minimum Level - Normally if they don't have the minimum level, look no further. But if they are off by '1' level (e.g. minimum is lvl55 and they are lvl54), don't rule them out. Take a strong look since they might be a few points from hitting the minimum.
2) Layout - This tells a lot about how much they know about defense. If they surround their camps with walls but leave their gold/exlicer bins in the open then you can probably say they aren't very good. If their wizard towers and mortars are not upgraded then they don't understand splash damage. Etc.
3) Antiair - This is an important factor when it comes to War. Many people like to air attack (e.g. all dragon attack) and if their antiair is low then they will cost the team stars.
4) Town Hall (th) Level and Experience Level - Normally a good indicator but not always a guarentee. A level 50 player should be an upgraded th6 or medium th7. If they are th9 then chances they gemmed or th rushed. Once again, this doesn't rule someone out assuming they have upgrades to match th level.
5) 'Friend in Need' - This is in their profile. If it's <1,000 and they are lvl50, that means they don't donate. Very bad for the clan since they will leech off others and will be eventually kicked. Ideally 2,000-5,000 should be what th7 players should have (assuming they aren't a gemmer).
6) 'Nice and Tidy' - This is in their profile. This tells you how long they have been playing. Although not entirely accurate but an active person playing for 5 months should have 400-450 out of 500. If this number is really high then they had an CoC account for 1+ years (doesn't mean they were active). If it's really low but their th level is high then chances they gemmed or th rushed.
7) 'War Hero' - This is a recent stat with the introduction of Clan Wars. Although still new, if a player has 50+ points then that means they have been in a few wars. Remember each war you can get a maximum of 6 stars/points. Assuming they had 60 points then they have been in a minimum of 10 wars.
8) Builders - If they are all busy then that shows they are actively upgrading. If they are idle it could mean several things such as inactivity. This doesn't rule a player out but something to take notice if there are lvl 1 archer towers and cannons that should be lvl5+ while gold bins are full but workers are idle.
Once again, these are things to look for. Start with the first item and work your way down. If you see they fail to meet many of the criteria then these are warning signs that the player is someone you will eventually kick. Save yourself the trouble and don't even invite/accept them.
Hope this help.
(The original posting of this blog can be found at http://cocunmatched.wix.com/clan )