There are a plethora of YouTube channels dedicated to Clash. Some are pure entertainment, some offer very useful guidance, others a mix of the two. The ones I recommend here are good channels for helping you up your game. There will be other good ones out there I've missed, but in general be wary of channels with staggeringly huge numbers of subscribers. They're normally trying to entertain in order to gain viewers and make a living than trying to inform. In any case, watch all vids with a critical eye, even the best YouTubers give bad advice occasionally.
TALES FROM SPARTA - Well, I dare say it's not the best channel out there, but this one features our own attacks, and hopefullyadvice geared towards our needs.
ONEHIVE RAIDS - An excellent channel run by an extremely good war clan. Features HowTo guides on everything war-related and lots of war recaps featuring and explaining good attacks. They are a little TH9 three star oriented, but they do have plenty of material for TH8s too, and have recently started featuring some advice for TH10 two star attacks.
CLASH OF CLANS ATTACKS - My favourite of the more popular, entertainment channels. Galadon is always upbeat, and whilst the content isn't quite as advanced or accurate as the channels from more serious war clans, amidst the laughs there's a lot of useful advice for people getting started with new attacks. Also a good channel for getting early news about game updates. Sidekick PETER17$ now has his own channel which can be good for some laughs.
SPENCER23$ - Leader of the clan Galadon is in, Spencer23$ isn't quite as prolific as OneHive Raids or Clash Of Clans Attacks above (who both do daily videos). But he is one of the best guys to watch out for new or unusual attack strategies from, like mass witch and AQ-healer. His videos tend to have a raiding focus rather than war focus; his barching max TH10 for 2 star videos are well worth a watch.
I also like POWERBANG who features content similar to OneHive Raids but with some non-war related stuff too, JTJ U who are a serious war clan but not quite at the top level so features some useful advice on less advanced strategies (although it takes a while to get used to all their made-up acronyms), GADI HH who hails from one of the few clans that ever beat OneHive and delivers interesting war attack videos, CHUCKY who has posted some war attacks I hadn't previously seen elsewhere, and HULK who posts lots of high-level war attacks and is credited with having invented HoLoWiWi.