So, anyone who has played in Table Top RPG campaigns for any length of time has probably had the problem of not having enough experience points for buying the things on your character that you think it needs. For various reasons, the way you're playing the character, the way you're rolling, the focus your character has put into something, you just feel everything should be a bit (to a moderate amount) higher, but you simply don't have the XP.
When you take this, and add to it that not many people like being branded a 'twink' and that in an intense game you can fall behind on your character's core functionality, it can be very frustrating to watch as all your XP gets gobbled up by the 'important' things like combat skills/stats and your 'character' skills and stats are left lagging behind. I honestly feel that if you're running things right the players should always be somewhere between the "I feel competent in what I can do" and "I need more to improve and represent things better" when it comes to experience, however sometimes despite your best efforts things will go too far one way or the other.
However, before I can go fully into what I'm talking about this, I need to define the two terms i used above, namely what I view as the 'Core' skills/stats of a character as opposed to their 'Character' stats/skills.
Core - Generally speaking characters have their core functionality that is separate from what they do for fun. If your character is a hacker, your computer skills are your core skills. If you are playing a fighter, your combat skills are your core skills. It's not particularly hard to find, your core skills are what your character brings to the table. If you talked about your characters with your group before hand, this is the role you play the "I'll be the fighter" vs. the "I'll be the medic" or the "I'll be the strategist". You'll know your core skills/stats, they're the ones you use the most (most likely), if you don't know them you may need to relook over your character and get to know them a bit.
Character - Contrary to what some say, your 'Character' skills are not everything that isn't a Core skills. There is actually a wide gray area in between for secondary roles, back up functionality, etc. For note, combat skills are almost never character skills. Why? Most RPGs center around combat, maybe not your campaign but the system itself. Combat is a function for someone in the group, and unless you have a game (i.e. the Hijinks system for D20) where actual fighting shouldn't be happening, combat probably will not be a character skills. Even more confusing is that some things that you may want to consider character skills may not be one.
For example, "Performance: Violin" is very likely a character skill in a lot of games. It isn't likely going to be important for the campaign, nor is it going to be the core functionality for your character. Your character is more likely to be the "Bad ass swordsman/strategist who also can play the violin" than the "Bad ass swordsman/strategist/violinist". That being said, look at those two statements, there is a slight but important difference between them that makes the difference. In the second one, "Violinist" is listed right with the two core functions the character has, where as in the first one it is clearly something on the side. Those skills on the side is what I mean when I say "Character skills"
The Difference - Quick and dirty the difference is simply that, if it is important to the campaign it is not a character skill. If it is vital to the character's functionality in the game, it is not a character skill. If it is something that fleshes out the character as a person, it may be a character skill.
So why do I care?
That is the question you're asking now I'd imagine, why should I care about this? You should care about this because 'twink', 'munchkin' and 'min/maxer' are taboo words in table top gaming. They're insults, essentially saying in one term the sentence "you're a roll player, not a role player". The words get bandied around a lot as cover all terms any time someone makes a particularly combat capable character, but not all combat cracked characters are these things which is important to know.
However, if you want to play a character based off Xena, Hercules, Achilles, Musashi, or the like in your weekly table top game, how do you prevent yourself from falling into that category? Well, mechanically the way to do it is to spend some of your precious points on things that do nothing that flesh out the character. Matsu Mesutsume is an expert spear fighter, perhaps one of the most dangerous women with a spear in all of Rokugan, but did you know that she can dance and actually enjoys the experience as much as she does fighting? William Hyde-Smythe is a noteworthy swordsman and a clever tactician, his ship is one of the most advanced in the world, but this rich boy turned adventurer can also play the violin, and often does so when he's bored. Both of these characters were built to be combat capable, in Mesutsume's case extremely so, but both are partially saved from being "twinks" or "min maxed" by the fact that they have other skills on their sheets, skills that serve no purpose other than to help define who the character is, what they've done and worked with in their life. It's a way, using only mechanical numbers on your sheet, to show that your character may be more than just a lump sum of mechanics and numbers.
Before I go on I just want to point something out. There is a difference between taking a Character skill to flesh your character out and make them more a person, and doing it to hide the twink status. If you ever catch yourself, even jokingly, going "I'm not a twink, I have dance!" you may want to relook at your sheet. Skills taken just for the purpose of obfuscating that almost everything else is in combat skills is not a character skill. There is a very very fine line in difference, but you want to be aware of it.
So how do I use this?
Using it is simple, while this is more on the mechanics for the character, think about those side skills you are taking. Why are they there? What do they say about your character? Answer these questions and you've just used them. Their entire point is to help you flesh out your character, giving you things to spend points on that aren't just your character's core functionality. Once you are taking skills that do nothing but help define your characters, you're already using this.
Yeah, but XP is tight and the game is dangerous
The problem of not having enough XP for your character is a common one, especially when you want to flesh out your character while still doing your whole core role. After all, if your character is made to be the ultimate spear fighter, and you are having problems staying ahead of the other players in spear fighting, are you really going to waste XP on side skills when your core character defining trait is at risk? No, not likely. So how do you do it then?
My ultimate suggestion is to ask your GM. If the skill really doesn't do anything for the character aside from help flesh them out, ask the GM about it. They may surprise you and just let you assign the skills a bit. Now, they probably won't keep doing this (the point is to show that you care about more in your character than just their core stuff afterall), but once or twice,here and there they may let you slide. Just don't expect those skills to really benefit you (counting towards ranking or what not) as you are getting them for free.
The other way to do it is ask the GM if you can do something to earn more XP specifically for side skills. Now while this also kind of falls under something for nothing, it also works against it. Keeping an IC journal for instance makes you flesh out your character more. If your GM is paying you for it for side skills, well the purpose is still there right? So talk to the GM about it, they may help you out.
A Note for GMs
So, moving onto the GMs now, if you want to encourage people to do this and flesh out your characters you need to be more proactive. There are a couple things to do, one is tell people they can get extra XP by keeping an IC journal. Give out XP specifically for buying side skills. Alternatively, just randomly reward people who are doing things on the side with free ranks in the side skills that are relevant to them.
The point being is that mechanically you need to encourage them to do it, and give them the tools if you want it to happen. XP is precious to player characters, and in games, especially ones with a high danger level, it is very hard to not drop it all on things that keep your character alive. So give them a way and the tools to encourage them to get those side skills. Reward them if they try to use those skills creatively. If you encourage the development of characters that are more than just numbers on a sheet, your players will reciprocate and give you just that. On the other hand, if you just want filled out character sheets for a dungeon crawl, well, go with that.
Either way, the power is in your hands to either encourage or restrict this as the GM for the game. Use it wisely.