I remember being a high school reader in history. I suggest relating to some of the following sources:
- Always read stuff you find engaging. This might be topically (revolutions) or chronologically (the 1950s) or spatially (post-war France) or transnationally (the Indian Ocean trade system). You might not be aware of some fields of history, such as social history, cultural history, women's history, labour history, economic history (not as dull as it sounds!), religious history or sports history. There's a lot to hold your attention out there.
- First year University textbooks written in the UK. They contain narrative, primary and secondary sources, as well as prompts. The ones I've seen tend to be about 100 pages. These provide a basic survey of the variety of stuff below—they introduce you to the idea of studying history seriously, rather than as a curriculum enforced to meet nationalist indoctrination needs. AFAIK the A level system in the UK is designed around preparation for University, and prefers developing real skills to nationalist mythology. Still includes nationalist mythology though, a more advanced kind based on cultivating liberal-democratic individuals, etc.
- Sourcebooks. Collections of documents from the period in time. These vary in quality and availability so I'm not going to recommend one. If you must have a recommendation then I would suggest Wendy Lowenstein's Weevil's in the flour, an oral history of the Australian depression, as experienced by the working class and petitsbourgeois. Sources vary in quality, part of reading sourcebooks is learning to analyse when sources are lying, the result of a limited perspective, the result of bias, not useful in other ways, or learning how to read useful stuff out of otherwise tainted sources.
- Substantial monographs. I'd suggest reading at least one. And I don't mean Beevor's Berlin. I mean something like Thompson's Making of the English Working Class, Braudel's The Mediterranean and the Mediterranean World in the Age of Philip II, Hobsbawm's Age of Extremes or Bloch's Feudal Society. This list is biased towards Marxist social history. You'll soon discover that Marxism is central to historical methodology. Unlike popular non-fiction, these works grapple with an issue historians consider significant and do so using advanced methodology. For example, Thompson uncovers the meaning of pre-modern working classes by examining methodist frame knitters. These works are normally considered highly influential in history par history, I haven't recommended works that are primarily theoretical (such as Braverman's Labor and Monopoly capital). If you can't get through one you pick (or get advice on picking one more specific to your interests), at least read the introduction, the first chapter, the last chapter and the conclusion. Also remember to use the table of contents and the index.
- At least one academic journal article a month, until you know what to read. For starters, I recommend EP Thompson's "Time, Work-Discipline and Industrial Capitalism" which was originally published in Past & Present (IIRC) and is available free from the journal, or here: Libcom. Journals I recommend include Past & Present, William and Mary Quarterly, Labour History, The American Historical Review. This is of course off the top of my head, biased towards my interests, etc. New Left Review used to have some great stuff in the early 1960s. Historians publish long findings or long topic surveys in monographs (books). Historians publish provisional findings, or smaller findings as journal articles or chapters in thematically collected books. Reading journal articles, especially from recent journals, will show you the cutting edge of historical research.
- You need to learn how to cite. I recommend Turabian or Chicago manual of style. (If your teachers want a different citation style, they'll tell you and hopefully supply a citation guide.) You need to learn how to take notes. In your notebook remember to write a full citation of the source you're reading, and include page numbers next to your insights, paraphrases or things to quote. There's no point quoting without citing who said it or indicating the page number they said it on. For example, a full citation of Braverman above would be something like: Harry Braverman Labor and Monopoly Capital: the degradation of work in the twentieth century New York: Monthly Review Press, 1974. You need to learn how to use Google Scholar and library catalogues (worldcat for example) to find material. Wikipedia can be a useful point to start to raid their source lists, but the sourcing quality of historical articles in wikipedia is incredibly poor (the sourcing quality of most encyclopaedia articles is incredibly poor).
- Finally, the process of history is one of interpretation and evaluation. Once you've worked through some of the above, I suggest getting a University textbook on "historiography" which is the method of writing history. Largely this is a debate about what valid interpretations can be drawn from texts. You'll notice that some academic journal articles are called something like "Review Article: Hate in Europe after WWII" this means that they're reviewing the historiography of writing about hate in Europe. They're not actually going to advance opinions about the history of Hate in France, but are going to talk about how people have written about hate, and what their major findings are. Review Articles are awesome.
- And if you get through the above and have time to spare, find a local archive and get permission to read 15cm of archives of a person or organisation. Organisational or personal documents are very different primary sources to newspaper articles, or reminiscences. They're very different to "selected" sources in sourcebooks, for one, archives may never have been read by a historian before. They can also be considered "dry," but I've never gotten through 15cm of letters without having at least one good insight worth writing up. Prior to the 1950s most archives will be manuscript or handwriting duplicates, after the 1950s most archives will be typescript or type duplicates. Archives are normally kept private for 20 or 30 years. Most practicing historians deal with archival material, others deal with oral history (like Lowenstein above), finally a smaller group of historians produce synthetic histories based on the archival or oral work of other historians.