Opening note: I am a chaos magician so all my opinions are from the lense of chaos magick
Grimoires can be quite different, but usually have sections on the theoretical underpinnings of the magick, and then the magick itself (rituals, seals, and the like). Some grimoires will also include some basic rituals for raising energy, invoking, banishing, the basics. If you already have your own rituals for these things then you don’t need to switch them out to use the magick in the book.
Magick is often times only a part of a larger religious system, so you will likely find yourself drudging (or maybe not if you into it) through lots of religious jargon to find the information you’re looking for. I think it’s fine to skip most of that stuff as you don’t really need it to work the magick and it’s filled with religious dogma and limiting beliefs. With more modern grimoires, this isn’t really as big of a problem.
Reading grimoires is a very time consuming but rewarding activity, given you actually use the information you learn from the book. Some books will feel like their all fluff with very little of practical value, however it’s important to note that length of a books content isn congruent with the use you can get out of it.
For example, I recently finished reading the Arbatel, a short grimoire that really only had about 8 things of practical value, the sigils of the 7 Olympic spirits, and a seal that’s meant to help you contact the angel that oversees whatever concept you ask about. The 7 Olympic spirits are widely known to be some of the easiest spirits to work, and being able to contact the angel over any concept alone makes the book worth the read. The book was only about 60 pages long, and the seals made up less than 2 of those pages, so the ratio of pages read to usefulness isn’t exactly equal.
So anyway that’s all I have for now, if you have any questions feel free to ask, please be well.