Are you talking solo or what? In general, if you shoot and you are not using a suppressor, you are basically hoisting a flag saying here am I. Sometimes you gain more by waiting to shoot if you are not guaranteed a kill. If you have a shot, take it but don't be surprised if you miss and the other guy turns around with his 8x Kar98 and headshots you.
In solo, if there are 4 left including you, I would stay low-key if you are not super confident in your aiming abilities. If you are cocky and good you can get the drop on people but it is very circumstantial because of where you are in relation to the blue circle and where it is going to end up. If you are at the very end with 4 players, then the circle will just close up to a point so that is about being stimmed up to your eyeballs and full health because the damage is so high from the blue.
Also movement is imperative, but of course if you are pinned what can you do? Drop nades (smoke isn't always reliable, because it seems it is very client-side), you can snake in the grass but if someone is above you, it is easy to spot someone snaking. Have other people fight it out and then get in there to mop it up.
In duos and squads it is very important to flank. Have someone lay down suppression and then run in defilade to flank the enemy.
In this game every thingis fair I think except of course the stuff that is against the TOS. Camping, crawling, hiding, going full aggro, sniping, guarding the bridges, hogging the circle, staying in a vehicle which has tipped over. There are pros and cons to every strategy.