I'm a sucker for a system. I rarely worked on scales when I was young, and it's obvious why - there are too many options. They can be fast or slow, tongued or slurred, one or two octaves or full range. There are majors and minors and chromatics, and if you want to get into arpeggios and broken chords there are all kinds of diminished and augmented and 7th chords you could play. All with different articulations, different speeds, different emphasis. I could spend days worth of practice time just trying to get a thorough scale workout, and therefore I never ever did. Too hard, too overwhelming. This is why I love a system.
With a system, you can trust that over time you will get everything done. With a system, you can put in a reasonable amount of time every day and notice improvement quickly. With a system, you don't have to waste time deciding what kind of technical work to do on a given day. Just take the next page of your system. Give it 20 minutes, and even if it's not perfect, if you've put good energy into quality practice, you have certainly improved something. It will be easier the next time you get to it. With a system I can trust that scales are a life's work. I don't have to be amazing today, because next month I'll see this same page and I can rework it then. I can make tweaks to the system as I go along, to focus on the things that I feel weakest at - but basically I can trust that I'll be doing something every day.
A system is a lifestyle choice, really. I know people who go on and off diets, and their weight fluctuates dramatically depending on what they are allowing themselves to eat. My own preference is generally healthy eating and regular exercise. I can choose to indulge here or there, or choose to rest instead of running on a given day - but basically I know that my lifestyle is a healthy one and work within that. Similarly, I do some kind of technical work on the oboe just about every day.
Currently, I do the scale patterns from the Taffanel-Gaubert book, with a system by Michel Debost. The scale pattern itself is simple - it goes through every major and every minor scale every day, each in an 8-bar pattern that covers two full octaves. The system, though, is a list of 60 different articulation and rhythm patterns to apply to the scales. Every day I play all 24 scales, working through the system, and then I mark where I left off and pick up again the next day back in C major. I have to make a few adjustments because an oboe is not a flute - I play the B and Bb scales down the octave and skip the most hardcore doubletonguing patterns - but basically this works for me tremendously well. I can tweak it occasionally to focus on double or single tongue or speed or smoothness or dynamic, but if I don't have a specific concern in mind I can just zip through the system. It takes me about 20 minutes to play the day's scales and when I'm finished I have slurred, tongued, moved my fingers fast and slow, and played every note on the instrument both loudly and softly. In two days I get through all of the articulation suggestions.
Before I picked up this Taffanel-Gaubert/Debost system over the summer I was working from Marcel Moyse's Gammes et Arpèges. That book has 480 different exercises - scales, arpeggios, and all kinds of broken chord work. Finger studies, mainly. He has a list in the beginning - numbering every exercise in a not-quite random order - 1, 134, 267, 400, 53, 186, etc. The great thing here is that you don't just start with major scales and gradually get into harder and harder material and give up. His suggested order mixes everything up so if I just do three or four exercises a day I get through the whole book in about 4 months and no one day is particularly more overwhelming than any other. Again, I modify the exercises as needed to keep things in my range. Generally I'll go up to high A, but if I'm feeling unusually feeble or if it's one of the really tricky broken chord figures I might drop a few more high notes and not beat myself up too badly. After all, with a system I know I will see plenty more high A's later and can work on them when I feel more fit.
I worked from the Whitney Tustin Daily Scales book in college, and that's the book I'm sending most of my students to lately. In his system you do two pages of scales every day - one page of chromatic and one of diatonic. All of the scales are full-range - from low B to high F - and written out for the oboe, which is great because here again no one day is much harder than any other. If you have to go all the way to high F for every scale then Ab major is really no scarier than C major (except I suppose for the left hand Eb…) On each page there are a variety of articulations that you have to work through, all with the same notes. So you would play a full range chromatic scale with each of 6 articulations, then an F minor scale, say, with each of 12 articulations, and then you are done for the day. In 4 months you have worked through every major and minor scale and you start again.
I also have some younger students who are working in Gekeler Book 2, which has pages of scales and arpeggios in the back. To them, I would suggest assigning 10 minutes a day to scales. Start at the first page of technical work, and spend that much time. Flag the place you left off and start there again the next day. In a few weeks you'll be back at the beginning, that much more competent and ready to reattack C major.
The importance of scales is not just that my fingers become comfortable in all of the various major and minor keys, although that is a huge benefit. The point is not only that I am at ease in the extreme registers of my instrument, although that too is very important. I use scales also to work on basic articulation and evenness. The oboe feels and sounds very different in its various registers. A low Db doesn't sound anything like a middle B or an octave G# or a high E, and those notes resist the air in very different ways, too. I use my scales to practice neutralizing those differences, or at least concealing them. It is essential to be able to tongue effortlessly at the same length in every register. I work to not allow tension into my body even when the fingerings are hard. I want to be able to "type" out any articulation in any register without affect or stress. That way I can sculpt my musical phrase in whichever way I choose, and not be forced into a lesser choice by my inabilities.