I can only tell you what I did, which I think helped. I read. There’s no way around it. If you want to develop strong basics in philosophy, you need to read. A lot.
The question is what do you read. Many introductory courses and online advice repositories encourage beginning students to read classic papers. Personally, I have never been a big believer in this and found that reading introductory textbooks was far more helpful.
Here are some of the textbooks that I liked (follow the links for more information). I’ve rated the difficulty of the textbooks between * (easiest) and *** (hardest) stars:
Philosophy of Mind (Lowe)*
Epistemology (Goldman & McGrath)*
Philosophy of Science (Rosenberg)*
Philosophy of Math (Brown)*
Analytic Aesthetics (Dickie)*
Metaethics (Miller)*
Metaphysics (Loux)**
Normative Ethics (Kagan)**
A Blackwell Companion to Philosophy of Language (Hale & Wright)***
Philosophy of Language (Soames)***
Other resources that I found helpful include:
Philosophical Analysis in the Twentieth Century vol 1, vol 2 (Soames) ***
Oxford Philosophy Faculty Podcasts *
Stanford Encyclopedia of Philosophy *** (warning: this is a tool created for professional philosophers, and its articles are not always beginner-friendly)