We know that you -can- willingly go prone as a minor action, but we're unsure as to the mechanics of recovering from it. Does it matter if you are knocked prone or willingly make yourself prone? And how do you unprone yourself? Is it a minor action as well? Do you have to make a saving throw for it, since it's listed under Conditions in the PHB?
Standing up from prone is a move action; it does not require a save.
From the Rules Compendium, p233:
A creature can end this condition on itself by standing up.
From the Rules Compendium, p236:
Stand Up: Stand up from prone
It doesn't matter whether you were knocked prone or willingly dropped prone.
You can only make a saving throw to end an effect when the ability that inflicts the condition explicitly says that a save will end the effect. For example, if your ability inflicts
slowed (save ends) on a creature then it's slowed until it makes a successful save against the slow. If your ability inflicts
slowed until the end of your next turn on a creature then that creature is slowed until the end of your next turn; it cannot make a saving throw against the effect at the end of its turn.
There are a few distinctly different parts to this that work independently which you seem to be confusing together, so I'll break things down a bit so you can hopefully understand what's going on.
A brief word on conditions
Those conditions aren't necessarily things that require saving throws. What they are is just mechanically meaningful states for your character to be in. They're pretty much just a small bundle of side effects tied up with an easy-to-reference name. That's all they are!
How are conditions applied?
They can be applied through any means. They're just little bundles of mechanics that any part of the rules (or your custom rules) can utilise - for instance, being out in a snowstorm too long could just leave you slowed until you do something about it. Unless the rule in question specifies otherwise, the condition just happens and no saving throws happen.
Most conditions are applied by powers, and most of the time, those will involve a saving throw. I'll get into that soon.
How are conditions ended?
It depends on the condition. Conditions can finish as immediately as they can begin. If you're prone, then if you stand up, you're no longer prone, and that's it. Standing up is a move action, as Oblivious Sage mentioned, whilst dropping prone to apply the Prone condition on yourself is a minor action (as the rules say). Other conditions might end via other means, like Dying being ended by a successful saving throw, or someone using the Heal skill successfully to apply first aid to someone dying.
Some conditions, like Dazed, don't specify any obvious way to be ended. That's fine, because whatever applies the Dazed condition will normally say how to end it. Monsters powers may apply it temporarily, and that brings us to our next point.
Where do saving throws come into it?
In the simplest case: when a monster applies a condition with save-ends, e.g. "... and the target is slowed (save ends)." In this circumstance, at the end of your turn, you make a saving throw against that condition (and other conditions, one by one) and if you succeed at your saving throw, the condition ends. Note that if, say, a monster knocks you prone, this saving throw doesn't happen when the condition is applied - it happens later, at the end of your turn.
I'm discussing conditions in general, there. A search in the compendium suggests there is only one monster that applies prone with a save-ends. You'll generally encounter the save-ends thing with other conditions.
In other circumstances, if a rule specifies, you'll be required (or offered the option) to make a saving throw against a condition. For instance, there are various powers from classes in the Leader role that will let you make a saving throw on any condition for free.
Mind you, this isn't the only way applied conditions end. It's just the way that involves saving throws.
Some examples (and possibly restatements) just to offer concrete circumstances!
- You can apply the prone condition on yourself by going prone as a free action. You can stand up again with a move action.
- If a monster knocks you prone, you have the prone condition. At your earliest convenience (e.g. on your next turn) you can stand up again, because there's nothing stopping you.
- If a monster makes you slowed (save ends), you're slowed until you make a saving throw to end it (or something else ends it, such as a power that immediately cures this condition). At the end of your turn, you can make a saving throw to end the slowed condition.