TH9 is in some ways the most complex place to be. There are four different roles:
(i) Two Star Crew (targeting reliable two star attacks in on all but the easiest TH9s)
(ii) Three Star Crew (targeting riskier three star attacks on the TH9s)
(iii) TH10 Cover Crew (targeting one or two star attacks on TH10s when cover is needed at that level - generally very high-level TH9s only here, and only when a matchmaking mishap has produced a lot more enemy TH10s than ours).
(iv) TH8 Cover Crew (targeting three stars on TH8s that our TH8 crew have not three starred)
Most players will generally consider themselves in the Two Star Crew or the Three Star Crew, but some flexibility to move between roles is advantageous.
Note that since the Christmas update, TH8 and TH9 have become easier. This means that only rarely do TH8s need to be cleaned by TH9s. Sometimes some safe two stars will still be needed on mid-high TH9s (if there are a lot more TH9s than TH10s in war, or if we get a mismatch). But often the priority will be to pick up three stars and let the TH10s clean what remains. GoHoWiWi/GoHoWiPe or LoGoWiWi/LoGoWiPe can be a good compromise between a safe two and trying to get a three. But don't shy away from learning the all-out three star strats like GoHo and GoLaLoon. You'll get a few fails along the way, but three stars count for a lot more than two stars at the end of war.
TWO STAR CREW: Target getting safe two star attacks on bases that aren't easily three starred. Whilst ideally the two star crew will work it's way up to the top of the enemy TH9s, cover is normally available from the TH10s so start on lower bases and work up. If all bases are sorted before you use your attacks, switch into one of the other three roles.
THREE STAR CREW: Target getting three stars on bases with weaknesses. We seldom need to three star all TH9s to win a war, so start on the easier bases and work up to the higher bases. In some situations you may need to switch into one of the other roles (for instance to provide cover for the TWO STAR CREW having a bad day).
TWO STAR CREW: Aim to be achieving two stars on over two-thirds of your attacks. Consider this when assessing which base to hit. If you're consistently falling significantly below this mark consider targeting lower bases, or ask for advice.
THREE STAR CREW: Aim to be achieving three stars on around half of your attacks. Bear this in mind when selecting your base. Low-percentage long shots may have their place at the end of a war, but early in war there is just too much risk of this wasting one of our strongest attacks. If you're consistently falling well under 50% success rate, consider targeting lower bases or switching some of your attacks to safe two star strategies.
TH10 COVER CREW: Success will depend on the war situation. You may be trying to sneak a cheeky one-star on a very high level TH10 by either charging into a non-centralised TH or picking of outer buildings for percentage. Alternatively you may be trying to two star a low level TH10. If you reach the point of being able to do that with some consistency, you are probably ready to head to TH10.
TH8 CLEAN-UP CREW: You should be three-starring the base with nearly every attempt when performing this role.
The typical two-star attacks are GoWiPe or GoWiWi. On some bases Dragons may viable. Lavaloonion can be a two-star strategy but is different from the three star approach. Other less common options exist like AQ-Healer, Giant-Healer, Giant-Wiz and GoVaPe.
Note that GoWiWi is the most likely of these to yield a three star attack, and on some bases (particularly those with very few compartments) can be considered an out and out 3 star strategy attempt.
Note also that the mass dragon attacks that you used to use at TH8 are generally not able to three star well-designed TH9s (your AQ, extra dragon and extra spell do not make up for the higher defences, xbows, extra AD, extra air mines and the enemy AQ which is as deadly to dragons as an AD). Target bases for which you can reach the town hall with your dragons without coming under fire from one or more of the air defences. Attack from the safest approach (as opposed to at TH8). Upgrade your dragons as early as you can.
If you're doing a GoWiPe or GoWiWi type attack on a lower base than usual, that you might reasonably expect to destroy over 80% of the base consider bringing back-end hogs or loons to help clear the last line of defences. This can help nail a bonus third star, but take care you don't put the two star at risk.
Whilst there are occasionally other options such as Mass Witch, GoVaLo, HoLoWiWi, PentaLavaLoon and, for vulnerable bases, some of the two star strategies, by far the most common three-star strategies are GoHo and GoLaLoon. The exact nature of these attacks vary depending on the base.
Three starring all but the weakest of TH9s requires a comprehensive analysis of a base and a real understanding of the attack strategy you are using. Crucial elements are:
(i) Lure and kill clan castle (have a good plan for this, failing here ends your attack)
(ii) Kill enemy AQ (she does huge damage to defence targeting troops like hogs and loons since they won't target her until all defences are down)
(iii) Do any other preparation needed (e.g. for hogs, you may need to pre-trigger a double giant bomb, or take out a few defences so that your main hog force pathing is predictable, for loons you may want to kill an exposed air defence)
(iv) Launch main attack (e.g. for loons, aim for one lavahound per AD with a spread of loons that will target separate buildings while under the hound protection, use rage to get to the ADs quickly except for the last AD which may need time to pop your hounds to get the clean-up pups)
(v) Save a few troops for clean up if this is likely to be necessary, particularly on higher level TH9s time-outs are not uncommon; be sure to have a plan for those corner builder huts and the like.
Aside from TH10s with no infernos or infernos so ludicrously positioned you can ignore them (in which case normal TH9 strategies apply), there two types of TH10s you can attack. Those with two multi-target infernos (use very high HP troops that can withstand the infernos for a long time, GoWiPe heavy on the golems and pekkas is probably best, I find 4 Earthquakes and 2 Rage works well), and those with two single-target infernos (use lots of low HP troops which the infernos can't get up to high dps on, Giants, Valkyries, Witches, Hogs, Balloons are all options - I'd recommend something like a Giant-Valk-Wiz composition with lots of heal spells or a Mass Witch attempt, Barch can also be viable but you're likely to be asked questions if it goes wrong!).
Initially when in this role just use whatever you used to favour as a high TH8. With the extra troop space, AQ, and spell, your attacks are significantly more powerful than they used to be and you have some margin for error. Upgrading your dragons will make performing this role even easier. Once you have unlocked Lavahounds and L6 Balloons this is worth considering as it is massively overpowered at TH8.
The Two Star Crew should try to get most of their attacks in as early as possible and ideally not leave any attacks until the last six hours of war unless you are able to switch into one of the other TH9 roles.
The Three Star Crew should try to hold off on their attacks until a good proportion of the rest of the clan has attacked. This will enable you to judge whether you need to be ready to do a TH8 clean-up, or a Two Star Crew clean-up, or a TH10 cover attack rather than go for a three star on a TH9. Less experienced, or less successful, members of the Three Star Crew should be particularly ready to switch to the Two Star Crew or TH8 Clean-up Crew when the war situation demands it. More experienced or successful members of the Three Star Crew should save their attacks until late in the war, ideally the last six hours. As well as being able to slot into other roles if needed, this gives the other Three Star Crew players a chance to try to three star the easier bases first. However, if you are one of the lowest attackers left to attack, don't hold back your attack longer than necessary as this may make decisions difficult for the remaining TH10 crew.
As discussed above there are various clean up roles you may need to step into. Know which ones you can take on, and which ones you can't. Only very flexible players who can perform a wide range of strategies, and can plan new attacks quickly and effectively under pressure should wait until the last few hours of war. Additionally players who are able to gem troop armies are an asset here in case last minute changes are needed after there is time to cook the required troops.
Don't rush through TH9. Take the time to upgrade all your troops, walls and heroes whilst slowly upgrading your defences. Give yourself time to master your chosen strategies against opponents of your defensive strength. When you are nearing the point of upgrading to TH10 you should be able to two-star low-level TH10s with L1 inferno towers and TH9 level defences. Look for opportunities to practice this in wars that are clear wins or losses already.