Tower victory is my favorite now as I tend to get bored fast in the end-game conquering all cities especially if I cant raze them
There are two ways to achieve tower victory imo :
Builder:
Firstly use religions. Up to prince I am able to grab all religions but one (usually) depending on other leaders.
Found the religions, breed great prophets: build all wonders with +great prophets points in the GPP farm (with enough farm and production). Use the great prophets to build the religion wonders.
If you get another type of GP you can use them as well as alternate (veil building with scientist, etc).
Grab as much land as possible at the beginning, and plan on settling near raw nodes (in the big fat cross or just one tile outside it).
The first nodes you build are: life and fire
Then go mind, body and enchantement (if you dont have them from palace).
Then rush the soulforge, get entropy and chaos mana (and shadow now too? council of esus wonder or node) to build the tower of necromancy. Thats welcomed death mana.
If you get too short, use the ritual of oghma thingy.
When you are set, prepare to defend when you build the tower of mastery
This is almost like a domination victory actually. Only easier.
The best civ for this used to be amurites because the palace offers mana not obtainable through religious wonders.
I never use the crap amurites civ spell as I find it stupid to destroy all my pretty nodes and my mages dont need the crap exp it gives (raging barbs/close neighbours and fire balls are all you need).
Amurites civ spell is really the crappiest of all, btw. Make it +1 free level to all arcane units or something.
War-monger:
Now sometimes at prince I cant grab enough religions. At monarch I can usually get max 3, so I go for either the "good" or "bad" ones :
OO, veil and esus OR runes or leaves, order, emp (if possible for emp, if not its no problem, emporyan religion and sun mana are crap).
So wait for other civs to found the religions and go annihilate them.
Top priority is to get OO first, if you cant found it, go grab the holy city.
Then found yourself or grab runes and leaves as soon as they are founded. Earth mana does give chances to discover more ressources and nature mana to breed druids or nature III archmages to improve land.
Only after focus on getting other holy cities.
If the religion is founded too far, like on another continent, just grab (alot of) land and create the nodes you need.
Its really just planning ahead and scouting what other leaders you have and where the holy cities are :
If you have clan/doviello leaders, cassiel or auric, you can found all the religions. Some other civs have favorite religions: dorf leaders always found runes early, elves found leaves early, etc. Scout your neighbours early, if you have elves as neighbour you can skip founding leaves for example. Trade for religion techs before attacking your neighbour.
If you have good leaders, you need to hurry the good religions, if you have sheaim you need to hurry veil, etc.
Some features also give mana like the tomb of sucellus (life), that fire pyramid (fire) and the broken sepulchre (death). Plan to grab these early as well.
In my 2 stacks of doom now I have highly promoted units with city attack, 2 lichs (fire+death maxed), 2 fire+death archmages (not maxed), 1 buffing archmage (with haste, courage, enchanted blades and valor), stack defenders (like guards), heroes and assassins.
Scout ahead and blast them damn assassins.
You will loose mages to assasins, the trick is just to build alot of adepts early and go make exp on barbarians with them (one fire ball then attack), these mages are just waiting to fill the spots of the dying archmages
Last tower victory at prince I ended with almost 1 mana of each type (no sun tho iirc) + the standard 3 fires and 3 death (huge map).
Tower is more suited for standard and up maps. For smaller maps, I have no idea.
My games always end in a mixing of conquest/domination/tower victory.