When do you upgrade items and when do you upgrade the citadel?

Different DGs use money diferently. TB and QoT should be spending a lot on upgrades since they are more skill based. Reg for instance should be spending most of his cash on items since he is very dependant on items.

In general get the building health ASAP since buildings do not heal without it. Get the first gold ASAP as well. It helps to keep your creeps upgraded as well, but that varies by game.

Currency 1 and building 1 are both the most important upgrades early on.  Later, you should upgrade reinforcements up to either catas or giants all at once(a slow progression towards them will simply feed the enemy).  If you need priests, get your general to buy it.

Translation: how do i get good at demigod?

Most of the upgrades at the citadel are not required, the big one to shoot for is catapultasauri, which you can't get until war rank 8.

So, I normally spend the first 10k solely on items, with the next 10k on catapults/giants. 

My first priority is basic staple items, like mana regeneration and armour.  Maybe move speed or a healer idol depending on my DG.  I then get some of the low-end citadel upgrades, particularly the ones that improve building HP/damage and the first level of currency.  I sometimes get priests if we have good DG's for pushing.

I then get a wide range of items under 2k.  Nimoth Breatplate, Wyrmskin Gloves, Vlemish Faceguard, all those great mid-tier items are well worth getting at their reasonable price.  The only item of moderate to high expense I consider early on is heart of life and maybe mage slayer.  Otherwise I don't purchase anything over 2k.

After I have myself filled out with decent items, I then balance my income between further citadel upgrades and item upgrades.  If I'm playing a DG like the UB, I'll focus more on item upgrades, and if I'm playing with someone like the QoT I'll get more citadel upgrades.  My needs in the present situation obviously take priority, but otherwise at this point it's about splitting my resources sensibly between these two priorities, neglecting neither.

It depends on the gametype as well. If you're playing fortress the building health upgrade should be the first one you get. Usually I spend the first 3k gold on items and then buy a citadel upgrade or two, such as gold and experience. Since I play as the UB I focus more on items.

But whatever you do, don't buy priests early game. All you're doing is giving your enemies double the experience.

The game type will decide this too. Obviously on Slaughter you need to worry more about health boosting items than citadel upgrades, where as on Fortress the building upgrades are essential to victory. The other DGs make an important factor here too. If you know know you are up against TB getting Priests will just feed him. If you are facing Erebus the same rule applies. If your enemy is spamming a Heart of Life then angels will drive him nuts.

Now it will change with every match but if you feel confident with just a teleport scroll I recommend getting Structure I as soon as the match starts, on all games but Slaughter. You'll be able to creep up your gold pretty easily but having your structures regenerating from the beginning of the match will help deal with the little damage enemy creeps do to it over time, and will often deal with the slower start.

Basically it all depends on the game. If you are getting chased down and auto-attacked to death get boots of speed (or a wand of speed) and HP boosting items. If you are running out of mana and going back and forth to base get the Battlecrown and the Vlemish Faceguard combo. For a bit over 3k your mana problems will be mostly solved. If you find yourself not doing much damage buy some gloves to compensate. If you can't do that last bit of damage as they run away the Wand of Speed is great for a chase down to get off the last attack. When the enemy gets a Heart of Life it's practically required for you to get one as well. Regardless of what your output is the thing will heal them faster than the crystals in your base.

Overall, in the ideal situation your opponent should be the one pondering what item or upgrade purchase will help the most, as when you have the advantage of acting first, your opponent will be on the reactionary side.

Priests do little more than give your opposing team more gold if you're not ready to buy catas any time soon.

But early on, the 3 important upgrades in order of priority are: 1st building health, 1st gold, 1st xp. Other people mentioned the first two, but the experience one shouldn't be overlooked: it can make quite a bit of difference.

I try to be a team player by spending gold on citadel upgrades whenever I feel I can, especially if I have an early kill. It's hard to balance, but sometimes for the sake of a cit upgrade you just have to forgo an item upgrade or even a potion (which might cause you to have to teleport back earlier than you would otherwise).

I'd recomend this thread for tips on when to upgrade the citadel

http://forums.demigodthegame.com/348575

I think he meant get an idol, since Idol priests don't give xp or gold.

I'm actually surprised at how effective some of the early upgrades end up being.  Tower Damage doing AoE damage  is very solid at keeping your defenses alive, as it often doubles their damage output against Grunts.  It also makes it easier to run behind your defenses when being ganked, since they can ward away a persuer that much better.