Scarves are probably one of the first projects we were taught in school. And other things that only require straight pieces to complete like some traditional socks and tank tops. After that socks and hats are probably some of the easier projects! Hats are super fast to complete too.
Also watch YouTube videos at half the speed and copy their movements to learn the stitches and techniques! Very handy for me at least who learns best but copying and trying.
I mostly use 4mm 20cm needles for my socks. Size 5 for stuff like hats. Circle needles for scarves and blankets. But it depends on the tightness of your knit and your project and yarn strength.