When I try to apply socionics, I try to keep in mind what socionics is. (information metabolism; essentially, what people are aware of and focus on.) I then look for anything which might signify key aspects of an element. What does this person focus on? How do their thoughts reflect their focus? How do their actions reflect their focus? I try to get into people's motivations and thoughts and derive where those motivations might have come from. A lot of the time it's unclear as a single action could the result of many different motivations, and motivation from many different awarenesses. I keep in mind that getting into people's heads is not easy, and often impossible unless they're willing to bring you in. I rely on my ability interpret the reasoning of things and people's vibes, but it's a constant battle of building up and then breaking down the conclusions I come to. Over time I've begun to realize the impracticality of trying to do quick typings, and I only give typings weight in situations where I'm able to get really close to a person and be sure I know them at a deep level.
Really the only thing of practical use I get out of socionics on a daily bases is the realization that people just have different ways of thinking about things and a way to try to rationalize it. I might assign a type or traits of a type to a person in order to understand where their coming from and adjust my perspective in order reach a compromise in situations of misunderstanding or general disagreement. But, often these traits I assign to the person are temporary in order to get through the misunderstanding. Assigning a permanent type to someone takes a long time and generally just doesn't happen as it's too impractical to come to any finalized sense of certainty that I have figured out their true type. There are a number who I will give provisional types to, but they're all very subject to change, and I really don't give any weight to the typing making it essentially pointless.