I've tried dozens of todo apps and systems, and yet I was always coming back to a simple piece of paper is the digital version of that piece of paper
The four design principles
Put an end to big, demotivating todo lists
Start every day with a clean sheet
End each day with a feeling of satisfaction
Focus on the essentials, the rest is bonus
Make it easy to get started
Like peeling an orange, start with a small nip
Have a positive attitude
Celebrate each task finished
And this is how I got to these four principles

Start the day with a blank sheet

Every time I was using a todo-like system I ended up with huge lists.
At some point I'd give up and start a new list, endlessly repeating the same cycle. The problem was that those lists got to be so long that I didn't even know where to start. I tried priority tags, deadlines, categories, but it always ended the same way.
I now believe it's good to keep a list of tasks somewhere, but you shouldn't be using that list to plan your day. At the start of the day you should just write down what you want to achieve that day. Period. Simple, and effective.

Identify what's really important

If you don't know what you want to achieve today, how can you feel satisfied with what you've done?
That was the question I was facing during long weeks of preparing my thesis for university. Procrastination was taking hold, big time.
The thought of having to spend endless hours writing pages of text was simply so unappealing that I didn't even start.
So, I tricked myself. I told myself: even if I can get half a page done, I'll consider the day a success. I defined the minimum I wanted to achieve for the day.
And it worked. This decision allowed me to get started, and even better: I was feeling good about myself.

Start small, and use the momentum

If you've read the above, you might wonder 'so half a page was considered a success?'.
Well, yes, I did consider it a succcess. But what actually happened was that once I got started and reached my minimum goal for the day, I felt good. I felt in the zone. And just continued writing. Once I got started, it got easier and easier to just continue.
And the best part? All the work beyond the minimum felt like a bonus, making me feel even better.
I was no longer driven by the (negative) pressure to do some work, but by the (positive) desire to do more.

Reward yourself, you did a good job!

Finally, I believe that instead of feeling bad about what you didn't achieve, you should feel good about what you did manage to do.
There is no 'that's the least I should be doing', every task completed deserves its own little reward. This was where really improved on my piece of paper: it allowed me to design some small rewards for finishing tasks. I created a button that is satisfying to push and accompanied it with a little 'level-up' or 'applause' sound. It may seem like very small things, but I for one am always looking forward to pushing that 'done' button!