There is no recommended standard for track sizes. What track sizes you use mainly depend on the electrical requirements of the design, the routing space and clearance. Every design will have a different set of electrical requirements which can vary between tracks on the board.
All but basic non-critical designs will require a mixture of track sizes. As a general rule though, the wider, the better. That’s because wider tracks have lower DC resistance and therefore higher current capacity, lower inductance, can be easier and cheaper for the manufacturer to etch, and are easier to inspect and rework.
The lower limit of your track width will depend on the fabrication ability of your PCB manufacturer. Typically, figures are 10/10 and 8/8 for basic boards. The IPC standard recommends 4 thou as being a lower limit. The lower the track figure, the greater care the manufacturer has to take when aligning and etching the board, and this will cost you more.
As a start, you’d better to use 25 thou for signal tracks, 50 thou for power and ground tracks and 10-15 thou for going between IC and component pads. Good design practice is to keep tracks as big as possible and then to change to a thinner track only when required to meet clearance requirements.