This specifically relates to Werewolf: Wild West, but I’m aware that most WoD uses similar rules.
Aside from spending Rage points, the main way to perform multiple actions in Werewolf is to ‘split’ your dice pools by the number of actions you wish to take, simple.
But how do I handle actions which don’t require any rolls. For example; Moving, aiming, reloading and some Werewolf Gifts don’t have any dice-pools to split.
Aiming, the process of adding your perception dots to your shooting pool, is a slow process. I would not allow someone to aim if they were doing any other actions of significance. The whole point of that action is focusing yourself over multiple rounds.
Moving, in world of darkness, is free - up to a point. I don't think it's considered an action in the RAW, and so shouldn't impact this at all.
Speaking - another action that doesn't require a roll - is a thing you can do for free as well, to a point (I forget if this is RAW, or simply a house rule every ST I've ever known in twenty years has used, the amount of words you can use varies from ST to ST). Obviously you're not going to orate in a combat round, but unless your mouth is full or whatever, barking commands shouldn't interfere terribly with much, either.
Reloading - in the age of W:WW - is a fairly complex affair. There's no roll because it's simple to do, but time consuming. To hustle it up, or do it while multitasking, I'd ask for a Firearms roll, either Dex+Firearms if their actions are primarily physical in nature (reloading while brawling/dodging), or Wits+Firearms if they're reloading and the actions mostly require their focus. Maybe Strength+Firearms if their grappling and trying to load a gun (what?). In a more modern setting with detachable magazines, reloading is much easier to do under pressure and I'd make a judgement, as an ST, on a case-by-case basis.
Werewolf gifts without pools to split, it is my understanding, come under two types "simply decides to turn on or off at will" and "passively on." Smell of Man, for example, says that it's on/off at will. Things like this are simple enough that they don't need an 'action' per se, like uttering a single word, it's simply a thing a Garou can do without putting too much into it. Stuff that's passively on is also not an action, but I'm assuming you're mostly focused on the first type.
Any physical action after moving can be performed without penalties as long as the distance is equal to or less than half your maximum running distance. Performing an action while moving subtracts one die from the action's pool for every meter/yard moved.
Taking aim is part of the roll you use to fire the weapon. Actively aiming is different, the bonus you get is based on focussing on your target for a full turn, it cannot be performed as part of a split action. Reloading can be performed as part of a split action, but there is no official roll for it. We usually use dex+firearms difficulty (6 minus firearms rating) the player can allocate as many or fee die as he wishes as per a normal split action.
There are three types of action (pgs 268-270 WtA20ed)
Reflex: No roll required and free to take (eg. talking).
Automatic: This takes a full action and no roll required except under special circumstances. (Automatic action doesn't mean that it doesn't have a roll attached to it. It just means that it is normally not required.) Then like all other actions this takes an attribute and ability e.g. Reloading: Dex + Firearms, or Moving: Dex + Athletics
(Splitting your dice pool to perform multiple Automatic actions counts as special circumstances)
Fixed Actions: These are actions that always require a roll.
As per the multiple action rules, 20th ed take the lowest dice-pool and splits it amongst all the actions. If the story teller wants they may increase or lower the difficulty as well.
Loading bullets is covered clearly in Reloading (pg. 295 WtA20ed)
Qoonpooka's answer is very detailed and deals with all of the specifics. But, if you need a general rule, I think the right thing is to come up with rolls which you usually don't ask for each task, and then to split the0 dice.
For example, driving (in normal circumstances), reloading or calling with a cell phone are tasks simple enough, that they don't normally require a roll. But, if someone tries to do all of them at the same time he will possibly fail at least one, so you can make them split dice between, let's say Wits+Drive, Dexterity+Firearms and even Charisma + Expression.
Now, specifically, fast Reloading is covered on all the game flavours. In Wild West (page 239), a roll of Dexterity+Firearms is required at difficulty 6. Each success loads a bullet. In my opinion, difficulty 4 would be fairer. In W20 the rules are different, but since you are playing Wild West and I think you are looking for a general rule instead of a specific rule, I will not paste that text here.
