As you're taking notes, try to summarize what the source is saying without looking at it. This should help you paraphrase a little more effectively. (If you've got a very sharp memory, though, you might need a different strategy, or at least wait a few minutes after reading before trying to create your version.)
Try to bundle multiple sentences into your version rather than going one sentence at a time.
Once you've got a hunch that you'll be using a source, go ahead and create the citation for it.
As you take notes or start integrating information into your paper, you'll be able to add the in-text citation as you go.
If you write your whole paper, then add citations after you're finished, you're making yourself practically redo your research to figure out what came from where... and you raise your risk of accidentally plagiarizing something by overlooking it!
Make sure you know which information came from which source. Some suggestions:
As you get a feel for your topic and what you're going to say in your paper (that is, what your thesis/argument will be, and what major points of evidence you want to bring up), start building an outline so you can figure out the flow.
You can drop sources and/or quotes into it, as well, so you can see where you've used a source and where you might still need to do some more research.
As you check over your paper -- you're not turning it in at the actual last minute, right? -- look for spots you have quotation marks without any citation information close by. Paraphrased information needs citations, too, of course, but "quote marks" stand out from the text a bit more obviously as potentially suspicious.
Generally speaking*, paraphrasing is preferred over direct quoting. When you paraphrase correctly, there's a lot more room for your original ideas to come through, and your cited content can be shaped to fit into your argument more easily.
When you're quoting, keep it minimal -- just the most significant pieces that you absolutely cannot or should not reword because they'd lose their impact. You should always "pad" your quote with original phrasing to either introduce it and/or to trail off from the quoted piece. Another good rule of thumb is to include a sentence of explanation for each quote you use to unpack it a bit: don't just restate what the quote said (we already read the quote...) but to connect it to your argument.
*If you're analyzing a work of literature for English class, for instance, you'd want to use lots of direct quotes from the book. Less so for the secondary sources you're using to supplement your analysis, though, and your quotes should still follow the above advice on minimalism.
"A much larger analogue of the asteroid belt, the Kuiper Belt is a cosmic junkyard, full of rubble thought to be left over from the formation of the solar system. But whereas the asteroid belt is made mostly of rock and metal, objects in the Kuiper Belt are composed largely of frozen water, ammonia and methane" ("Two Years On").
The Kuiper Belt consists of icy chunks of frozen water, ammonia, and methane believed to be "leftover from the formation of the solar system," much like the rocky field of the asteroid belt ("Two Years On").
Though both the asteroid belt and Kuiper belt are believed to be remnants of the solar system's formation, the Kuiper belt consists mostly of ice rather than rock, including frozen methane and ammonia as well as water ("Two Years On").
A bigger version of the asteroid belt, the Kuiper Belt is a cosmic junkyard, full of rubble believed to be left over from the formation of the solar system. But while the asteroid belt is made mostly of rock and metal, objects in the Kuiper Belt are composed largely of frozen water, ammonia and methane ("Two Years On").
Just like a paper, your presentations need to cite sources -- both in a Works Cited/References/Bibliography list at the end as well as "in-text" citations on the slides!
There's not an MLA or APA "format" for presentations: you can use whatever fonts make sense and so forth. Just be sure to still thoroughly document your sources, and that documentation is what will follow a style guide.
Again, the whole point of anything you're doing is to show your thinking, your ideas, your understanding of a topic. Focus on you as the presenter. If you have a 10 minute presentation, most likely you shouldn't play the entirety of a 5-minute video from YouTube.
Plan on giving credit for your visuals, as well.
Good news, though! Presentations are aesthetics-centric in a way written essays are not, and the style guides don't really care how you put slides together. In the professional world, at least, an informal credit is often enough (e.g. in a small hyperlinked caption: Photo by user via Flickr). Double-check to make sure your instructors agree with that, however.
Arguably, that's better for more decorative images, too. If you're pulling in a chart or some other kind of information-packed visual, a more formal citation is probably better.
A common scenario: "Yay, I got a good grade! No need to read the feedback; I'm awesome."
Also: "Ugh, I got a ***** bad grade on this stupid assignment. I don't want to think about it."
Both completely understandable reactions will lead you astray.
Everyone always has room to improve. (Heck, we're going to keep coming back and tweaking this page, and we're pros.) Maybe you actually don't understand semicolons but it wasn't important enough to dock you any points... but wouldn't you like to know that was an issue so you aren't doing it wrong in the future? Likewise, if you scored badly, there's obviously some important things you haven't nailed down yet that you need to understand.
As we mentioned on the Myths page, most plagiarism is unintentional, caused by carelessness or ignorance. You're not going to flunk because you missed something on one assignment... but if you start a pattern of missing citations and your prof knows they told you before to fix something... well, that's something else. If you knew you were doing it, you wouldn't. So read that feedback when you get assignments back so you can know what you don't know!