So this came on the heels of the latest episode Princess Spike as well as seeing some comments -- be it here from people posting about it or from reviewers.

First off, I have to say that I feel for the fans of Spike who wish to see him develop and become a decent character instead of constantly being the butt of tired old jokes. These are the people who see potential in him and I've seen some pretty expansive interpretations that go into some fine detail, essentially cementing him as the seventh of the mane seven.

This blog/essay isn't going to be another explanation of what could be done with Spike's character (or lack thereof) but rather a framework you could use to make or arrive at something yourself.

Keep Track
That is, of what's already been shown. It may seem like a pretty daunting thing to do: going through episodes both of his own and that of others to see his best and worst moments but this is stuff people have been doing already. His MLP:FiM Wiki page has some pretty detailed information about how he's been depicted in a variety of ways; including but not limited to his personality and skills.

I would recommend seeing specific episodes if you feel it to be necessary for you to grasp specific things in detail. That is, if you need to see something as it happens.

Regardless, these are just suggestions -- a means to an end -- for being up to speed with how Spike's been shown to us in (and even out of) the show. If you have more effective means of getting a clear understanding of how Spike has been shown on-screen or even off-screen, then more power to you.

Ask Questions
Lots of questions -- about anything you can think of. It'll be up to you to figure out what questions to ask and why. Be confident in the questions you're asking even if it's unclear where they'll take you. If you have any doubts, do whatever you can the clear those doubts.

It could be something as subtle as how his color scheme may fit with his character, to more obvious questions like how his job as Twilight's #1 assistant may have developed his skills set. It can be as broad as what are the things he would spend his own time on or it can be as specific as what would he do if he were to see Twilight and Rarity have a heated argument about him having to make a choice that could benefit the one but adversely affect the other -- specific scenarios, in other words.

Another important thing to consider is that for every question there are answers and for every answer there may be questions. It's important to understand the implications the answers would have but it'd best not to think about the implications when asking the questions as that would more often than not keep you stuck. It's OK to be reckless here.

Answers Can Come From Anywhere
Some questions can be answered from things that happened or was said in the show. Some questions may need outside sources like what psychology might explain about his behavior, imply about his upbringing or vise-versa. However, something you can also do is fill in the blank yourself if you deem it appropriate.

Be Patient & Explore
Let's face it, without this, you're not really going to go anywhere. Building up a character takes time whether or not they already are established (for some reason it only now occurs to me how much of this also applies to building an OC...). This isn't something that's going to happen overnight and is likely to take months. Take your time with it. This is really more about the journey itself rather than the end result because it's about exploration and discovery rather than a logistics exercise to get from point A to point B. All you may have an idea of is what the destination may look like but you don't really know where it is or what you're going to need to do to get there.

Know When or if to Stop
Theoretically, characters can become infinitely complex and deep. Heck, some questions can be left open to leave room for future character development or for the sake of adding mystery. It is up to you to figure out where to draw the line and say: "This is good enough."

Lastly, be sure to have fun while you're at it