First of all in my opinion at least as important as paying enough taxes is the responsibility of the state (the politicians) not to waste the huge amount of taxes which they collect every year! In Germany for example, where I am living, are so many public construction projects (an airport, a railway station etc.) which never get completed and cost much more money than scheduled initially. When my own house was build workers were so ineffective to open the street in front of my house and close it again several times because they knew that anyway I have to pay for everything. As long as politicians aren't responsible personally for the waste of taxes that won't stop. Why to put more and more money in a holey pocket?
Apart from that I think that tax laws should be as simple as possible! If the state asks everybody (even my 94 year old grandmother) to make a tax declaration it has to be so simple that also everybody can do it without help (for which he has to pay again)!
My (personal) favourite tax model would be that there was only one single kind of taxes: a turnover tax for everything one purchases. So in this moment when you use your money you have to pay taxes. Of course this turnover tax had to be higher than it is now as it would replace every other kind of taxes. It should be higher for luxury goods than for things everybody urgently needs for his daily life. The advantage concerning crypto currencies would be that nobody needed to know how many you store anywhere: taxes anyway would only apply in case you pay for goods or services.
It would be that easy that no tax authorities were necessary at all anymore. :)