I have got very limited practice and music theory knowledge and I would like to start composing some rock music but I wonder what are approaches for it. Should I first learn music theory clearly or Is it okay to just go and follow a composition book?
Neither. Follow your ideas - make up words, make a tune to fit, find chords which work with that tune.
Composing a rock song isn't quite like writing a symphony! There are fewer instruments, and their individual jobs are fairly well documented and easily defined.
The actual writng down is a different matter, and if that's what you want as a route to the end product of someone else playing your music, then knowledge of theory and how to explain on paper so others can understand will be important: that language is universal, and without it, you may not be able to pass on all the information from your song.
Fair enough, you can probably show each individual what to do, it works, but it's time consuming, and often inconvenient!
Three things are important in composing. First, learn everything you can. Theory, harmony, counterpoint, orchestration, etc. apply in all genres. Second, listen to anything; listen a lot to the type of music you want to compose (at the time.) If you want to compose blues, listen to blues, for tangos, listen to tangos, for country, listen to country. Third, practice composing. Get a free (at first) software program and some music paper. Write down what you think you hear in your "inner ear." This way you get a feel for how to put parts together. (I used Finale Notepad which think is still available; it was the best free program at the time, and Finale later offered me the big package at student rates.)
It takes time. Even geniuses like Mozart went through a long learning process (his childhood pieces are better than my best but a long way from his best.)
Some things can be accelerated by schooling. It also helps to learn one or more instruments.
In this case, practice makes perfect! The more you compose, the better you'll be. Trust your own ears, you know what sounds good and what doesn't. As you go, you'll learn relevant composing conventions. The internet is a great resource for finding the answers to your composing questions as you have them. Listening analytically to songs, especially in a genre that you want to emulate, can be helpful. Depending on your preferred method of composing, it can be helpful to be able to understand sheet music, at least the most basic components, so that you can use notation software to compose with.
As the current answers suggest, there are different ways you can go.
I learned a lot of music theory, a lot of acoustics, a lot of physics, music history, analysis, etc., but there are two things that have made it possible for me to compose:
- Learning to play (and ideally sing) a LOT of music
- Listening to a LOT of music
Now I know that classical composers have been quoted saying you should never compose on your instrument, that you should be able to make the music in your head. That’s all well and good, but we’re talking about rock. In my very humble opinion, the peak of rock composition is having your guitar or bass on and someone yells out something from the crowd and you make up a song on the spot with lyrics, melody and chords based on what the person yelled.
You want your hands and mind and ears to be able to combine ideas from all of your influences in real time. The process of having a feeling, associating that feeling with different musical elements that you’ve heard or played in the past, and then synthesizing those elements and channeling that synthesis into your guitar, bass, keys, voice, whatever to produce YOUR statement on that feeling is the essence of rock composition. That whole process is fed by listening to and playing music that moves you, that you connect with. So that you can connect it all together inside of you and send it back out into the world complete transformed into something that only your mind, taste, and fingers could produce.
As you listen to and play other people’s music, start making your own. Don’t worry about making it good. Just try to find sounds that you like, or even love. Keep doing it every day. Give yourself 5-10 years. Find others to collaborate with. One day you’ll play something and be amazed that it came out of you. Record it and memorize it. Keep doing all that and the songs will just start to flow out of you.
Composition is a different skill from playing and from theory. They are not independent (getting better at any one will help you in the other areas) but none is required for the others. That being said, I have never heard of a rock songwriter who doesn't play at least some guitar.
If you do play guitar, and you play rock music, you have all the tools you need already to get started. Just noodle around on your instrument trying things you've learned from playing songs you like, and when you stumble upon something cool, write it down or record yourself playing it. Try to analyze the form of songs you like, generally you'll see a lot of verse-chorus type structures. Then, you can decide which of the parts you came up with sounds better for which section of a song, and find ones that go together well to construct a full song. Then just keep doing it, over and over. The single best thing you can do for your songwriting ability is to write songs. Anything else you do should be supplemental to that.
Theory and composition books will have limited benefit for most rock music. If you're looking at progressive, fusion, technical, symphonic, etc. then theory and composition books will be super helpful. But if you're thinking more classic, pop, punk, and the like, you don't need it, and many of the people who wrote and played in those genres didn't know much of it. Gaining knowledge never hurt anyone, and I recommend learning at least some basic theory just on principle, but as far as furthering your goal of writing rock music, it may not be the best use of your time to dive too deep here.
Especially be wary of composition books. There's a wide variety of different types of books and courses on the subject. Many of them are geared towards art music composition, specifically orchestral and chamber orchestral ensembles. If the book you get is too specialized outside of your area of interest, it will be of very little benefit to you.
If you don't play guitar, probably pick it up and start learning rock songs. If you're serious about writing that particular genre of music, it's more or less a requirement.