While batting and bowling gets most attention, most players spend the majority of their game time fielding. Their best position will depend on skills like speed, reflexes, strength and judgment.
Players who don’t have particularly strong or specific fielding skills will usually play in the “standard” positions such as mid-on or cover where they’ll usually be midway between the boundary and the wicket. (In limited over games, they’ll often be around the ‘ring’ that’s used for fielding restrictions.)
The most useful fielding skills in these positions are catching (particularly difficult catches of a ball that is dropping behind the player) and judgment in throwing the ball back. Players must quickly decide which end to throw the ball to get the best chance of restricting runs or getting a runout. The benefit of throwing to the closer end could be outweighed by the positioning and skills of the person who would receive the ball (eg a wicket keeper, bowler or a fielder who has moved next to the stumps), and the importance of getting a particular batter out rather than their partner.
Fielders in specialist catching positions such as slips and gulley, or “short” positions, need to have particularly quick reaction times. They’ll also need to be capable of holding on to a ball that is travelling extremely quickly and could hit their hands with a big force.
Fielders on the boundary (“deep” and “long” positions) may have specialist skills depending on the level at which they play. At an amateur or club level, this could be a place where less skilled fielders are sent, “out of harm’s way”.
At a professional level, these positions are better suited to players who can sprint quickly as, because they are further out, their “arc” covers a wider distance. They’ll need a strong but controlled throwing arm to get the ball quickly back to the wicket. They’ll also need concentration for catches. In this area they’ll often have enough time to get in position for a catch, meaning it’s more important to reliably avoid basic errors than to potentially make an extremely difficult catch.
Finally, boundary fielders should be skilled and practised at stopping a ball that is running along the ground to the boundary rope. This can include getting down on the floor to push the ball back to another fielder who can then take care of throwing it back to the wicket. Doing this without inadvertently touching the rope with any body part at the same time as touching the ball (which would concede four runs) is an underrated skill.