I honestly don't remember my mistakes when I started, but I can say that play was about 5 years ago much easier than it is now. Errors are not committed only the one who does not play.
When i first started playing poker my first mistakes were :
1.Overvaluing pairs against passive players
2.Too much slowplaying and not enough value betting
3.Poor decisions preflop
4.not being able to quit when i got tilt
Which were yours ?
Easier and much more fun too. My favourite hand used to deuce-tray (23) back then I couldn't tell you the difference between suited and off. If I got dealt 23 I was all in... winning with this hand was always spectacular.
These days I just can't get myself to play the hand anymore... it's loosing money. So I have to sit back and watch others who do dare... less fun.