Ive tried to make this a concise guide to provide new and even some veteran players with a good intro into the realm of Clan Warring. This is by no means a complete guide, as I'm sure will soon be noted in the comments section, which btw are quite welcome.
A> 1st things 1st; If you want to be a warmonger you need to be in an active clan you can count on for 90% participation or you may as well hang up your spurs now cowboy.
B> COMMUNICATION...PLAN your attacks with your members, don't be afraid to ask for advice or suggestions from your clanmates if you're not 100% sure you can zero someone... discuss where traps may be hidden, spell use, troop composition, you name it, there are no dumb questions.
C> This may be hotly disputed but as a general rule, I would advise attacking the hardest opponent you can reasonably assure you can zero and don't attack any target that has already been at least one starred unless that is your only option. Work your way from the bottom to the top, allowing your weakest members to be the first to cherry pick so your big guns can play cleanup if necessary.
D> Place your CC so that your troops cannot easily be drawn out. Defensive war CC troops should be MAX LEVEL types; wiz or dragons with support troops is generally your safe bet, as unchecked they will lay waste to attacking troops of any type.
* Note: CC troops deploy in order of type ie. in order of the housing space they occupy, (ever notice how long it can take for 25-30 single housing space units to deploy?) so having a few barb or archers in your CC can be beneficial in slowing down their deployment and force the attacker to waste extra fodder to make sure they draw out every troop in the CC or suffer the consequences as even a couple of wiz left unchecked can contribute greatly to your defense (Since they move slower than archers, I prefer to have 5 or 6 barbs inside and the rest maxed wiz).
E> If your base has weak defenses in relation to your TH level, make sure your use a DMZ type design to maximize your chances vs hogs and make sure your trap placement is effective; it doesn't cost you anything to re-arm em so make sure they are deployed where they WILL get used (doubled up giant bombs can mean the end of a hog assault)
* NOTE: A DMZ type defense utilizes a ring of non defensive buildings around your heavy weapons as a buffer zone to keep troops that target defenses on the perimeter. These include: Giants, Hogs, Golems and Balloons.
F> The easiest and most effective attack type vs all TH9 and lower defenses is Hogs and plenty of well-timed, well-placed heal spells.
G> In general, the most effective attack types vs TH10 defenses are GOWIPE, GOWIWI and the Dragon/Hog combo.
H> When attacking, the FIRST thing you have to do is draw out and kill the K, Q and CC troops, no exceptions. Use a few hogs to draw them out and isolate them, then a few wiz, barbs and a raged King can usually deal with them.
I> Spell selection is crucial: hogs need to be healed, dragons need to be raged, GO strats need a bit of both or a well timed freeze spell to assist the attack.
J> Units cannot be healed WHILE under fire from Inferno Towers; BUT, the damage CAN be healed once the IT targeting them is has been destroyed or the unit moves out of range of them so don't just write off your units if you see them under Inferno fire, they can often be saved.
I> FYI, the clan loot bonus is calculated by adding up the bonus' from the top two 3 star kills your clan achieves. But remember, you don't get the bonus unless you win the war, concentrate on victory first, the res reward remains as a secondary objective.