Anyone who practices will improve so even if you only practice a few times a week you will make progress. However, if you practice daily you will improve daily. Practicing is the most important part about learning music and the amount of time you spend practicing reflects your goals.
If your goal is to slowly improve you should make sure you get three or four good practices a week (I'll explain what a good practice is below). That is enough to make sure you are first keeping up any skills you have learned and to make some progress forward.
If your goal is to perform gigs on the side or have fun playing with your friends then you will want to practice more than that. Your practices will also need to include time spend in front of a mirror or practicing with a microphone or amp or time spent playing with others. While many musicians performing in bars don't need to practice regularly they already have put the time in and learned their instrument. They already memorized the music. You are trying to get to their level and need to put in more of an effort.
If your goal is to be a performer, recording artist, composer, etc where you make all of your income from music you should be practicing even more. You should practice daily. You should practice warmups, scales, technique, old music, and new music every time. You should spend time analyzing recordings of others as well as of yourself. You should be researching what it takes to make it in your chosen field. No one is going to hand you a job in any of these fields. You must work for it.
I know I didn't tell you how often to practice but use your goal as a guide for yourself. Life is about choices and how often you practice will determine what you can do with music.
What is a good practice?It is more important to practice well than to spend a set amount of time practicing. People who practice the same amount of time like it is a chore often are thinking about how much time they have left to sit there instead of what they are doing. If you are not thinking about what you are doing you won't be able to improve it. Focus your thoughts on what you are doing.
Typically you will need to spend time:
- Warming up
- Practicing Scales
- Sight Reading
- Reviewing older music (or an old section)
- Learning new music (or a new section)
- Singing while dancing
- Practicing with someone else
- Specifically memorizing a piece
- Singing while acting
But mostly you need to spend time fixing problems.It does you no good to play the same song all the way through if you have one spot you play wrong every time. Instead you need to focus on that one spot or any other spot that is a problem.
Let's say you can't sing the correct interval in measure 15. Start by singing that interval with a pitched instrument. Sing it over and over, record yourself, adjust your posture, take a better breath, bring the sound forward, sing it without the instrument, etc. Sing it until you can sing it correctly 5 times in a row. Now, add the next note or two after that interval. Sing it over and over until you sing it correctly (again 5 times in a row). Next add the note or two before that troublesome interval. You repeat this process until you can sing it correctly with a full phrase before and after.
Sometimes you won't fix it in one practice. Many times you can fix the spot but then the next time you practice it is incorrect again. This happens! Every time it happens you need to go back to how you fixed it the first time. Each day you will be able to fix it in less time than the day before. Now if your problem is more about getting something like dynamics where you then need to apply the same thing you just fixed to multiple phrases then take each one at a time and fix each one before applying it to all of the phrases.
Any way you look at it you need to think while you practice. A person who puts thought into their practice will make more progress in less time than someone who is just going through the motions.