"Wizards and Alchemists study their arcane craft in Towers. Tower populations are comprised of creatures bound into service by powerful magic, made on the spot, or allied with the town through ancient pacts. Tower armies have uniformly good morale and some of the best range attack units available." RoE manual
Some may find the information in this section subjective or irrelevant.
Tower armies have some of the best ranged-attack units available.
A good strategy for Tower is to upgrade Workshop as soon as possible in order to upgrade Gremlins into shooting Master Gremlins. With relatively fast Stone Gargoyles it is possible to form protective wall of gargoyles around a stack of Master Gremlins. This works especially good against wandering creatures. The downside is, that Master Gremlins only have 8 shots, which can sometimes run out. Additionally, casting Haste on Master Gremlins makes them typically act first.
Another useful strategy is to form few strong troops and to fill the rest of the slots with one (or few) Master Genie each. During the combat Master Genies' can use their special ability to cast spells on the strong troops to furthermore boost their abilities. This way it is possible to cast 4–6 spells per turn. This is especially useful when playing on Difficult/Impossible difficulty. Buy the Tower hero from the Tavern in the first weeks. Collect all Gremlins into one stack and upgrade them to Master Gremlins. The moment you can recruit Master Genies, fill the 6 other slots with one each, or make two stacks of Gremlins and use 5 Master Genies. With about 200-300 Master Gremlins you can defeat most wandering creatures without losses and your army is very cheap which lets you save Gold for the upgraded Cloud Temple. In the first round of every fight you cast spells onto your Gremlins until they got Haste and/or Prayer to be faster than the enemy creatures. Then they will get ~ 2 full arrow shots out. Because they often get Precision, Bless, or Frenzy as well, their attack becomes ridiculously strong. Mirth often boosts their morale to let them maybe shoot an additional time.
Tower's town defense is made easy by cheap, resilient, and rapidly growing golems. When defending in the early game, fill all slots of your town with equal numbers of golems. In the first round, spread them behind the walls to minimize the effect of area-of-effect spells like Fireball, Meteor Shower, Frost Ring, Inferno, etc. The golems also have a good damage reduction against spells so spells will not bring you down. Then, always defend and don't attack yourself. Your towers will take care of all enemy troops because it takes a long time to kill golems.
Giants are not much use until they are upgraded to Titans. In fact, they only have 150 health which makes them quite vulnerable. However, upgrading them is very expensive.
Tower towns are very powerful in the late game, and draw much of their lore from the "wizard" hero in Heroes of Might and Magic II. Their creatures and structures are fairly pricey and on maps with scarce resources, you may find it difficult advancing your dwellings and especially acquiring titans. One tip for the thrifty wizard is skip upgrading some of your low level creatures. Gargoyles benefit with a speed boost to obsidian gargoyles, and master gremlins are a must (the Workshop is very cheap to upgrade), but until master genies, most creature upgrades are not necessary.
The lookout tower is a very helpful addition in the early game (especially on small maps), and never underestimate the incredibly effective library structure. Despite its high resource cost, the ability to gain extra spells for all levels is invaluable, and secures the tower as one of the strongest overall towns in the game.
However, after assembling a decent army consisting mostly of Titans, Naga Queens and several other support units like a few Master Genie stacks to buff your creatures, you can defeat almost any neutral stack at the time, especially if the hero knows Expert Slow.
If you have in the army both Titans and Black Dragons who hate each other, be very careful, as the latter will deal 150% damage on their own Titans having attacked them by mistake.
Three ranged units and two fliers.
Blacksmith is producing Ammo Carts, which gives Master Gremlins, Magi, Arch Magi and Titans infinite shots.
Relatively slow town (fastest troops move at speed 11). Nagas which are often Tower's main power are among the slowest on 5-7 level.
Prior to their upgrade, many units have significant weaknesses, and basic Gremlins and Giants are on the bottom of their level.
Spellcasting of Master Genies is random, and they can cast a generally useless spell like Magic Mirror, a spell which doesn't make much sense in the current situation (e.g. Cure on a stack with 108 HP out of maximum 110), or even a spell which would be bad right now (Anti-magic, Frenzy).
The most expensive town to build up.
Apart from Dungeon, Tower is perhaps the worst town to play on Impossible level, as Mage Tower which is necessary for 5-7 level dwellings requires Mage Guild and every type of resources (in Dungeon, 3rd level dwelling takes all types of resources). The ability of Master Gremlins to shoot is a big advantage, though.
Playing against Inferno, beware of Efreet who can easily destroy your Genies due to 150% damage output. Efreet are one level higher than Genies (6th vs. 5th), and generally much stronger and faster. Moreover, Efreet Sultans have Fire Shield ability, which reflects 20% damage dealt on them. As any type of Genies deals 150% damage on any type of Efreet, the Fire Shield will therefore deal higher damage on Genies.
3rd level creatures' dwellings on the map are guarded, which may cause complications in the early game.