Once you’ve decided on how to go about your bowing and fingering to a certain degree ( although you may change them later on ), you need to practice the bracketed part until you are fully confident with yourself.
If you feel that you have successfully mastered the bracketed part, then add a few bars preceding and following it and make that into one phrase. Play the whole phrase and see if you can still play the bracketed part without an error. It is a very common phenomenon to make the same errors in the bracketed part again as soon as you add a bit more bars. You were able to play it so well before,but all of a sudden, you make errors again. Why does this happen? Take a moment to figure out the reason. Is it the bowing? Or is it the fingering? More often than not, you may be able to solve the problem with a very small change you make.
Here’s an important tip for you. When you make an error, you need to think why it happens. To keep practicing without thinking about this actually has an adverse effect. It is almost like practicing to make the same mistake.
When practicing a new piece of music, first you should try playing it in a slower tempo than the actual one. See where you made mistakes and put brackets on those sections. Then you can start practicing focusing on those bracketed parts. We call this “Partial practice”.