k so.. like nobody plays QoT much anymore.. but in case you want to know if you get her on random or want to try her out.. she's definitely underestimated.
1. Shamblers
2. Shield
3. Ground Spikes (GS)
4. GS II
5. Mulch
6. Shield II
7. GS III
8. Shamblers II
9. Save
10. Mulch II / GS IV
11. Shield III
12. Shield IV
13. Entourage
14. Save
15. Mulch III / QoT Ultimate (don't remember the name...)
16. - 20. Entourage to Tribute, Spike wave
There is some wiggle room to get spikewave / shamblers II earlier.. spike wave earlier if your team needs the slow to catch people for kills only. Shamblers earlier if you're finding you're mulching often. Sacrifice shield points to get these earlier.
Spend all of your alone time in closed for to regen mana fast and to aoe creeps. Ideally you should fight in a creep wave, and GS the enemy and the creepwave at the same time. This provides a double benefit.. armor debuff + dmg on enemy, and all your creeps will now focus the enemy.
If you're expecting a long fight over a yellow cap or to get the flag in your lane, shield first, then walk up in open form. Ground spike and gogo. Just stay in open form so you get full benefit of GS attacks, by the time you change to closed form you lose out on most of the benefit of GS debuff (you don't attack when switching forms, and it takes a couple seconds). When you need to get away, stay in closed form and shield / mulch as necessary.
If you're left alone in a lane, GS the tower and rape it.. it drops very fast 
Don't run back to base early on if you're oom... just sit in closed form and regen quickly (+50% mana regen). On that note, don't spam abilities if there is no need, they're very costly. For example, if you can push someone out without needing to shield.. don't waste the mana using shield. Unless you're at the crystal, don't shield people when no one is attacking. If a beast is spitting and backing away.. don't bother shielding yourself until after lvl 7, your monks can heal it up. Don't constantly summon shamblers.. you only need them to mulch (summon them then), so unless you're at full mana and can recharge most of it, don't bother summoning them away from the crystal. Shield / summon shamblers when you shop. This all cuts down a LOT on QoT mana issues.
Favor: Blood of the fallen. There are some others that work out alright as well.. but none have the tanking power, which is what qot is really good at.
Items: For Blood, I'll usually buy vlemish helm first. This + closed form is a LOT of regen. Banded / scaled are great.. and then unbreakables sometime in there. If you're finding you need a LOT more mana than health (usually only in 3v3 situations), then pick up plenor for a 3rd helm. That's situational.. otherwise my next purchase is nimoth chestplate. Eventually I'll replace scaled with plenor but it's usually not a priority. Siege dems are nice if you have the cash and aren't left alone to take down the double side towers (if you're left alone, GS will rape them fast enough that siege dems are pointless if you still need gear). I rarely ever get Siege dems tho. Typical order:
1. Vlemish
2. Unbreakable boots
3. Banded Armor / Scaled Helm
4. Nimoth Chestplate or Plenor (depending on what you need more)
5. If Nimoth.. sell scaled and get plenor.
Late game hungarlings, journeyman's treads, godplate. Whichever you need most.
Mulching: It costs 250 mana to do mulch @ 10. That's 1500 hp and 500 dmg for 250 mana... RIDICULOUS. It can be reallly hard to kill a qot w/ mulch. Shield, summon shamblers / mulch, shield again, mulch, shield... They get off cd when you need them pretty much. You don't really need a sigil in 2v2.. but 3v3 you should 
You can take most people 1v1 if you go blood (even beast!). Other than what I've said above, there really isn't a lot more to qot.. item choices are situational.
Additions: I've been playing ALOT of QoT lately. Some more things to note as a result. The main reason I think people think qot sucks is because they just don't understand how incredibly powerful mulch is. I never did until playing her within the last 2 months. She has the best survivability of any demigod when focused. Sedna can heal for 1500 every 7 seconds @ 10. QoT can heal for 1500 every 7 seconds AND shield for 1450 dmg every 7 seconds @ 10. That's just ridiculous. With that in mind, you can simply tank alot of dmg if need be. And people just don't realize this. They will pursue a qot who's below 1000 hp thinking they have an easy kill.
Luring: With the above in mind, luring has become valuable to me. I'll start leaving a fight even if my mana isn't low but my health is. People follow into double towers thinking I'm oom. Then I shield / mulch up to a good health pool and turn around to chase them back or my teammates port in and we double up. I really think the major advantage of QoT at this point is that people are so used to seeing a weak qot or no qot at all. They just assume she sucks because nobody plays her. Use that to your advantage 
Ranged demigod tactics: If there is a melee demigod you can't push out just by walking up and going at it, soften them up a little bit. Hit them at range. When they push into you, retreat back into the towers. Get a feel for when they turn around. Turn around at that point and start attacking again. You can whittle down a beast / oak / ere and get them at a lvl that you can walk in and push them 
Battle tactics: You're not sedna. You provide much more benefit to your team if you ground spike the enemy and attack them than staying in closed form and spamming shield. If you're getting focused, it's different. Stay in closed form, spam mulch / shield and absorb the dmg so your team can attack at will. If they change targets and shield is close to coming off cd, wait and shield that person, but then get back into open and continue ground spiking. Some people might not grasp this.. just tell them to pretend your occulus or something and don't have shield. If they get a shield, great! But they shouldn't expect it. Again, you're not sedna. Also, if you're not getting focused but you're getting low on hp (to the point where they could switch and almost catch you offguard), go to closed, mulch, and shield the focus target.
Replays:
http://www.gamereplays.org/demigod/replays.php?game=51&show=details&id=133199
- A great example of a mana heavy build. I used plenor, vlemish, and hungarlings so I would always be able to push sedna out of lane and still be able to follow up on a tower. I ended up pushing several people out of the lane prior to going back. Also a good example of what to do when you're the focus of multiple people. Start running back to the crystal in closed form, spamming shield / mulch the whole way back. It works wonders. Also, I mistakenly grabbed something else @ 10 instead of mulch II... meh.
http://www.gamereplays.org/demigod/replays.php?game=51&show=details&id=133260
- Only 2 helms this game, and it was plenty of mana for what I needed. Got more armor than usually to deal with reg aa / tower hits / spirits. A clear example of when spikewave is better than another point in shield, but I got it way late (would have been 2-3 more kills... w/e).
http://www.gamereplays.org/demigod/replays.php?game=51&show=details&id=133264
- another 3 helm game w/ hungarlings. Very useful against an all minion char. Spam ground spikes to kill them off and shield / mulch to have the strength to still manage to push towers. 190 favor as qot in reg / sed / qot vs oak / ere / reg.
I ramble. Hooray.