I'm currently prototyping a turn-based tactical game. Most similar games that I've played or heard of (sadly, mostly the latter) structure turns in one of two ways:

Action Points
On each turn, units are alotted a quantity of generic points, which players can arbitrarily spend on movement, combat, etc. In some games, attacking always uses up a unit's remaining points.
Phases
Each player's turn – or sometimes a whole round – is divided up into separate phases in which players can only take one type of action. Usually there will be, at least, a movement and an attack phase, in that order.

What are some of the strengths and drawbacks of each of these schemes, are there any other ways you know of to structure turns, and which one would you recommend?

I like the action points method better because the flexibility allows you to do more clever strategic things. You can also automate moving units to the appropriate place from which to launch an attack chosen by the player. Phases can be confusing because you have to know ahead of time what action you want to take with every unit so you can move it to the right place from which to take that action.

An observation on Action Points, which are an abstraction of Actions/Turn; it's the inverse of Turns/Action, where an action is accomplished over several turns.

If action points are usable for any action -- this isn't always the case, they are sometimes further broken down into "general", "movement", "attack", etc. categories -- then one advantage of the system is that you can still choose the type of actions you wish to take if your actions have been limited. It's common in turn-based games to be able to suppress the actions of an opposing player -- "cannot act during movement phase", "loses 1 action point", etc. -- and unlike being suppressed by phase, a non-total loss of action-points may still allow a choice of action-types.

An advantage of phase-based play can sometimes be in the simple and obvious triggering of timed actions. An ability might trigger at the beginning of movement phase, or at the completion of the attack phase. With a point-based system, you're either more restricted to "at begin of turn" or "at end of turn", or have to go more complex with "at specific action type".

I like both types of game-play if implemented well in a fun game.

An observation on Action Points, which are an abstraction of Actions/Turn; it's the inverse of Turns/Action, where an action is accomplished over several turns.

The two can combine well. For example, take an action this turn which sacrifices 8 AP now to give yourself 4 extra AP next turn. Or, a certain ability can only be used every N turns, regardless of whether you have the AP to pay for it.

Either is fine, but I feel that the phase approach is easier to understand and exploit. It's still fun, but I end up plotting complicated strategies on paper or in Excel rather than in-game. At the same time, an action point system might be harder to balance-- if you under- or overestimate how many points an action should cost, the action becomes overpowered or impractical, respectively.

Another possibility is Time Units (as in X-COM). It's very similar to action points, but allows a bit more flexibility for the player and is more intuitive than the less-precise action point approach.

I vote for new Firaxis X-Com's Time Units. It really streamlines the whole gameplay without sacrifacing any decisions (actually, this simplification allows more decisions). Instead of counting all the time how many APs you have left, you just decide what you want to achieve.

On a sidenote, turns can be resources/advantages as well, in some games characters have speed or initiative that allows them to take their turn, so higher speed allows more turns. As an extention to this, to add in extra strong abilities i would have a character "prepare" one turn(possibly taking his next turn earlier) so he can use the stronger ability once.

On another side-note:most turn-based games use mana to perform most actions instead of action-points(1 action/turn, X mana the whole battle or more if you defend often or something)

I vote for new Firaxis X-Com's Time Units. It really streamlines the whole gameplay without sacrifacing any decisions (actually, this simplification allows more decisions). Instead of counting all the time how many APs you have left, you just decide what you want to achieve.

Pardon my gushing, but: They're amazing, right? In X:EU, you only get two actions per turn, but you still have essentially the full flexibility of the original UFO:EU (except, of course, you can't shoot before moving). Technically, it's just AP with the "attacking ends a unit's turn" restriction, but it's interesting because there are just enough AP to force you to carefully budget them while still having so few that you can instantly know whether you can or can't do something, without having to look it up. When combined with the movement radius your troops have, the effect is to move the focus from when things happen to where.

It's like how the original Command & Conquer was able to have a relatively deep strategy game with fast-paced, engaging action, without making the player internalize a dozen spreadsheets and a whole keyboard of macros, just by giving the player a clean sidebar and a single, contextual mouse button. Or how Deus Ex was able to turn a stealth-focused FPS into a deeply customisable, pseudo-RPG experience with several skills, measured on a scale of 1-4, a handful of binary augmentation choices, and a limited inventory.

On a sidenote, turns can be resources/advantages as well, in some games characters have speed or initiative that allows them to take their turn, so higher speed allows more turns. As an extention to this, to add in extra strong abilities i would have a character "prepare" one turn(possibly taking his next turn earlier) so he can use the stronger ability once.

You mean like Final Fantasy Tactics (and probably a myriad of games I'm not familiar with). That is an oversight on my part, but in my defence, I hadn't actually played that game until a few days after posting.

On another side-note:most turn-based games use mana to perform most actions instead of action-points(1 action/turn, X mana the whole battle or more if you defend often or something)

I'm not sure I've heard of this one, before... What's an example? Also, what happens if both sides run out of mana without destroying the other? Does it double as morale, and the side/unit that runs out retreats/surrenders? Or perhaps they fall, lifeless, like robots without any battery power?

I'm not sure I've heard of this one, before... What's an example? Also, what happens if both sides run out of mana without destroying the other? Does it double as morale, and the side/unit that runs out retreats/surrenders? Or perhaps they fall, lifeless, like robots without any battery power?

I'm quite sure almost any game(including FF:T) that uses magic uses this, except, they usually don't set it up that you have to be extra-carefull with your mana.

When running out of mana, mana-abilities(spells) become unavailable and characters have to use less effective attacks/actions.(hitting the opponent with your wand while not wearing any armor)