Start by plotting in your lectures and exercises, as well as other “non removeable” things (ex weekly scheduled sport).A good way to visualize/plan your week is to plot all the important/compulsory stuff first, so you know how much free time you have for: study jobs, leisure, study groups, sports etc.
Then you plot the things you know are coming - maybe it is not in this specific timeslot, because it can change from week to week, for example meetings with your study group. But once you have calculated the hours, it is easy to move the hours to another day.
Now it is time for an important and very individual side of schedule planning - your time used on studying. How many hours do you think you will have to spend weekly studying for lectures and groupwork for you to be "satisfied" with your own efforts?
It is also important to take into consideration rather there is a subject that has proven to be more difficult than expected and therefore requires more preparation?
This number of “studying hours” you then indicate in the plan – again the important thing is just to visualize how many hours you need to use. You can always swap it around between the days, so it fits whit your unforeseen plans.
Here you can also consider rather it would be more beneficial for you to keep your weekends free of studying or if you would like to have some of your studying hours removed from the weekdays. Hereby you can free up more time for a student job/or volunteering.
Or maybe you just want a greater possibility of "maneuvering" during the weekdays, because you then have more weekly free time, due to the involvement of your weekends.
You now have a realistic overview of how much time is left for volunteering, student jobs and other hobbies - which can then be plotted into the remaining time gaps.
You can find a schedule here.