If you're in a clan, it's good to share troops; the more troops you share, the more you are likely to get in return.
Upgrading the clan castle is a good idea as it's a great way to improve your offense without spending any elixir.
Train troops before you are about to attack with full army camps so that when your attack is completed, additional troops while be trained during the attack; thus, resulting in less time spent waiting for troop production.
Your village cannot be attacked by other players if you are online.
Single player mode is also a good way to earn gold and elixir (especially the higher levels).
Vary your troops that you use to find a combination of troops that compliments your playing style. Once you find a good combo stick with it until you unlock another troop. Try troops out.
You can also remove bushes, trunks, and trees for occasional gems.
Pay close attention to upcoming updates as several can be highly beneficial to you. For example, SuperCell often reduce the amount of gems it costs to boost production type towers for a varied amount of days.
SuperCell's clash of clans updates can be found on their Facebook page here.
When trying to recruit members for you clan, try the global chat in order to spread the word.
Offering positions such as clan elder can make new members more inclined to join but makes you seem desperate for members.
Join ClashTillUBleed or War Till UBleed.
If battles are getting too hard and you find yourself losing resources instead of gaining any, just drop down league(s) till your comfortable with the battle selection.
You can find all the queries, questions and other doubts related to Clash of Clans on official forum