I'll categorize this list into "good for physical health / looks" and "good for mental health". During lockdown it's really important to consciously take care of your mental health as the lack of daily social interaction can lead to feelings of social isolation and a lack of connection.

Physical Health / Looks

• Take care of your mental health It's a well known fact that mental health issues result in physical issues too and vice versa.
• Meals Eat a proper warm meal at least once a day. Bonus points if you cook it yourself and use seasonal fruits / vegetables! There are apps you can use to find out which produce is currently in season. I use a seasonal calendar app from the F-Droid store, but chose your preferred one. It's also really helping when you're wondering what you should cook if you want to cook. Find out, which vegetables are in season and then look for nice recipes for them!
• Nutrients Make sure you have no lack of nutrients, if so, take dietary supplements when the doctor says so (especially relevant for vegetarians / vegans -> B12, Iron, Calcium, Omega 3, ...)
• Skincare Establish a personalized skincare routine to use the quarantine time to finally get rid of those Acne! Your routine can be however you like it whether you prefer to just wash your face every morning and evening or want to use special products to treat skin problems like Acne or Dryness. Read skincare guides to find out which kind of skin you have (dry, oily, mixed, irritated, ...). If specialised skincare products for your problems don't seem to work after even weeks of using them daily, maybe you should try out going to a dermatologist to get your problems checked as there could be underlying health issues.
• Going outside This one is really hard during lockdown cause why should we go outside in the first place, if it's so much more comfy to stay at home all day long, right? It's really hard to establish the habit of going outside and take a walk regularly but you really should try it out. It's good for your health on all levels, physical and mentally. Breathing fresh air makes happy and helps you clearing out some cloudy thoughts you might have that day. If you don't know what to do outside, just grab yourself some music or an audiobook and walk around in the next park ~
• Sports ... I am definitely not the right person to suggest things you could do to get motivated for sports. For me it has to do with how every sports I am interested in is currently either not possible (Ballett, Swimming) or makes no fun alone (Martial Arts). I am trying to find a solution to it but.. yeah..
• Sleep Establish a good-night-routine with alarm clocks to help you going to sleep and waking up at the same time every day. What I currently do is 1. my skincare routine 2. a cup of herbal tea. My alarm for doing these things is set up for half an hour before I want to be laying in bed. A good night routine really helps you to get into the mood for sleeping which is not so easy to achieve especially if you're a student.

Mental Health

• Take care of your physical health Every point that's listed up before here definitely plays a role for mental health too as a bad physical health can result in a bad mental health and vice versa.
• Have a conversation with a nice person once a day Maybe you talk with your flatmate(s) or maybe you talk with your friends online. It doesn't have to be a meaningful conversation, but just talk about S O M E T H I N G. Make sure you have a healthy amount of social interaction despite lockdown making it difficult. Problem is that for some people (including me) talking online doesn't provide me the same amount of emotional bonding as talking in person, so I need to talk even more with people!!
• Take your breaks If you're working from home you could easily overlook taking your breaks as the borders between private and professional are less obvious. The result is obviously stress. You should try out using alarms for this one too! When taking a break, maybe you'd like to drink a cup of tea and hear music or draw something. Everything meditative works! Whatever makes you feel calm and relaxed.
• Hobbies Try to find something where you can be creative. Only watching movies / shows, reading and playing (not creative) video games (creative video games definitely work as a canvas for your inner creativity) can make you feel numb and bored out. I am currently into Fashion, Fashion Fotography, Skincare, Coloring and thinking and learning about problems like racism and feminism while trying to form my own opinion on those.
• Journaling You don't have to write some next level writing skills' essays about deep philosophical connections in the world, there are a lot of different forms of journaling, they all aim for the goal of helping you to self-reflect and getting some structure into your day to day life. Especially the structure part is really important during lockdown when it feels like every day is out of touch with your life. You might consider looking into:
  • The traditional journaling - the usual writing about topics that keep your mind busy. This one also helps your writing skills as you get used to transform feelings into sentences.
  • Bullet journaling - this one is highly flexible to your needs. You might want to look into the original bullet journaling method by Ryder Carrol (he wrote a book about it but you can also find summarizing articles and video essays if you're not concentrated enough to read a book) but you should also get inspiration by other bullet journalers as in how to customize your own journal so it fits your needs better. I for example neither use the yearly overview nor the daily or the classical weekly overview. Instead I organize my weeks by topics I need to work on. So instead of dividing a weekly overview into week days, I divide my weekly overviews into my study courses/modules and side jobs I have. It helps me so much more finding the information I search when I plan what to do for the day. Habit trackers are also nice as you can completely personalize them to your needs and they don't require much effort to maintain each day. There are also artistic approaches to them but be careful to not become perfectionistic here. It doesn't help you if your bullet journal looks beautiful but you're afraid of using it / it doesn't fit your needs. I might write a post about general bullet journaling tips and things to try out and all. In general - get inspired by other people but never think you'd have to use your bullet journal in a specific way
  • Scrapbook or Art Journal - this one is the most artistic journal you could probably have apart from a sketchbook. Here you can freely express yourself with scribbles, colors, stickers, your photos obviously, patterns, stamps, glitter pens, newspaper clippings, printed out recipes, articles or pictures from magazines, etc. There are tons of guides for it out there for you to find some inspiration. Best paired with a polaroid camera or a photo printer if you like these things. :3
  • Spiritual Journal - if you have some kind of religion you can use a journal to connect to it. Be it something like a Devotional Journal or a more pagan Book of Shadows like thing. I am not the right person to ask about how these work but if you're interested you can easily search for these kind of journals online too to find out more.
  • Mindfulness / Gratitude Journal - these are especially targeted towards a better mental health. Basically you write down every day some things you are thankful for or that were good that day, mostly "banal" seeming things like "the look out of the window" or "a friend complimented me for x". You could also use an Affirmation Journal for collecting quotes and positive beliefs you want to integrate into your life!
  • Journal with writing prompts / suggestions / activities to do / etc. - if you're not that creative yourself and really really don't know what to write or scribble or whatever each day, you could try out buying one of these journals where you get some different topic each day suggested to write about or to do, etc. They're really beginner friendly as you might notice that you could talk about some topics more and would like to talk about these more. They also give you conversation topics as you might want to discuss some topics with your friends!