Philosophy, per Wittgenstein's phrase, a language game: it is something we do with and about language. Philosophy is unique in that the rules of the philosophy language game are (part of) the subject matter of the game. So the "rules" of the philosophy language game are just really a starting point. I will link to few if any actual philosophers here; most of what I'm talking about is common knowledge and common sense, the rest is original.
Our starting rules divide philsophy into five broad categories. The first is epistemology: what it means to say one "knows" something. The second is ontology: what it means to say something "exists." The third is ethics: what it means to say something is "good" or "bad." The fourth is aesthetics: what it means to say something is beautiful. The fifth, and where philosophy gets all self-referential, is metaphysics: what it means to say something "means" something. Note that our starting rules are part of metaphysics, as are the general (but by no means uncontroversial) use of ordinary deductive (syllogistic) and inductive (empirical) reasoning.
I place epistemology before ontology on purpose, although the order is by no means uncontroversial. I think we construct our ontology, our picture of existence, to explain and interpret our knowledge. Others prefer to go the other way: we can talk about what we know only in terms of what exists.
One big problem in philosophy is foundationalism: what gets accepted as true "by default," and what can we do with that foundation. Remember: deductive reasoning requires premises, which are accepted as true "outside" the syllogism. Inductive reasoning requires facts; our inductive reasoning seeks to find the simplest theory that explains the facts. Premises are thus the foundation of a deductive system, and the facts are the foundation of an inductive system. It is perhaps possible to eliminate foundationalism entirely, but these systems quickly become highly weird.
Several distinctions pop up often in philosophical discussions. The first is the objective/subjective distinction. The philosophical canon uses these words inconsistently, so I will disambiguate them explicitly: Objective refers to the "real world outside our minds"; subjective refers to the content of a "mind" irrespective of the "real world." The concept of a "real world outside our minds" requires more elaboration, which I will discuss in more detail later. The concepts of objective and subjective can be expanded: for example, intersubjective refers to something in many minds at once; relationally subjective refers to the interaction between an object in the real world and our minds.
One way the objective/subjective distinction is used ambiguously is to use "objective" to mean consistently determinable. For example, it is consistently determinable that 2+2=4. It is also consistently determinable that if you divide a shape up into an infinite number of pieces in a specific way, you can construct two identical copies of the obect with the same volume as the original. Whether the consistent determinability of a concept implies something about the real world outside our minds requires linking the distinct concepts of consistent determinability and objectivity. In contrast, arbitrary means that any answer will do; for example, I can find broccoli tasty while you can find it disgusting without any contradiction or conflict.
The alert reader will note that I've said nothing about truth. In all my years of studying philosophy, I've never seen a useful definition of the word "truth," and it appears that I can do all the philosophy I want without ever using the word except as a philosophically trivial constant in formal logic.