Reddit mentions of A Little History of Philosophy (Little Histories)

Think about it this way: Reading primary sources that require previous knowledge to understand before you have that knowledge removes an entire level of appreciation you could be having for the work. Almost to the point to where reading it now would likely be just as valuable as not reading it at all. You're effectively paying your respect to their work by learning it properly.

I think it's important to distinguish your reasons on why you want to learn philosophy. If your main goal is to learn as quickly as possible, then contemporary books are the best. In anime/VNs/storytelling, it sounds cool to say "I've read the entire works of Plato, Descartes, and Kant," but in real life it's usually the single worst way to learn philosophy, and definitely won't do their knowledge justice.

Aristotle's teachings are over 2300 years old. We've had a lot of time to think about what he's said (much of it incorrect). On top of this, different philosophers have studied different fields. Just jumping from philosopher to philosopher won't do you any good, since each are likely going to be talking about very different topics. For the record, it takes about 4-8 years of university study to really digest everything that's happening in a single field, and there are over a dozen of them.

That being said, "The Problems of Philosophy" is a good general introduction to the concept of philosophy. A Little History of Philosophy is a personal choice of mine. Just remember, there are no shortcuts.

I don't study philosophy academically at the moment although I did take a course in A-level philosophy which I have just finished. I currently and previously only studied out of interest (I'm also 19). And I haven't been doing so "properly" for that long but perhaps that will help my answer a little bit.

Argumentation

As for the first question, it is fairly important to understand the basics of argumentation. In reading philosophical texts you want to be able to "extract" an argument because most don't provide or describe arguments in simple syllogistic form (that is, with premises and conclusions clearly laid out in a list). Most arguments are 'within' the text, often mixed in with lengthy defences of certain premises or elaboration on the meanings of key words used in the argument itself. Learning a little bit of propositional logic might be helpful. It's fairly straight forward and intuitive to learn about the different kind of argument structures you'll be encountering. Being able to look at a text and then reconstruct the text as a kind of structured argument is a learning technique I've seen used a lot.

Reading Recommendations

As for reading, it really depends on what you're interested in. I can't really give you recommendations based on the information you've given because philosophy is a gigantic field. Like, gigantic. If you can think of a thing, there is probably a "philosophy of" that thing. Case in point. But that's not particularly a problem. What you should probably do if you're not so sure of what areas of philosophy you're interested in is read some introductory texts that take you through many areas and see which catch your attention. These texts will often point you towards the key ideas in those areas of philosophy and recommend further reading of the big players in those areas.

Frequently I've seen recommended, Think by Simon Blackburn. You may also consider An Introduction to Philosophy by Paul Nuttall or Philosophy: The Basics by Nigel Warburton. The first real read I had in philosophy when I was younger was A Little History of Philosophy by Nigel Warburton also. None of these texts are exhaustive, of course. They simply open doors.

I might be able to recommend other reading if you say you have some particular interest in philosophy. Otherwise, those are good introductory texts to philosophy as a whole.

What do I wish I was told when starting to read about philosophy?

To be honest, I wish that it was made clear how important our intuitions are in philosophy. I came from a 'background' in enjoying sciences. (Background maybe isn't the right word since I was fairly young but I liked science). My interest in philosophy was perhaps mostly spurred on by my growing interest in the sciences. They grew up together, lets say. I liked science because I liked having good reasons for beliefs about profound things. Since I didn't see the use of intuitions in the sciences, I believed out-right that intuition should be avoided as a basis for reasoning. Now I see how absurd this is. Philosophers spend a lot of time considering what makes something rational or what kind of justification for our beliefs are good and which are bad. Intuition is something we come equipped to these discussions with and is something we are forced to work with and you should make friends with it.

Don't get me wrong, I don't think the processes of science should be heavily relying on intuitions. But intuitions are very much required to 'kick-start' philosophical inquiry. And it took a while for me to really deal with this.

Maybe there's other stuff I would say too, but that's the big one. I have unambiguously thought to myself before that I wish I was told this and forced to deal with it earlier on in the process.

Edit: Added in the advice section.