The second way to practice your aim is to run around and find scavs to aim at. Most of your engagements can be in close quarter combat which is a great simulation for the real game. Don’t forget to bring your favourite optic with you to practice.
To become more efficient at training against scavs, you should focus a good amount of your time on hip firing. Against real players, you may encounter each other at surprising times. When this happens you won’t always have time to aim down sights. So practicing hip fire against scavs is a great way to prepare for real players. You can start off by practicing with a laser sight to get a feel for where your bullets will land while hip firing. Then when you are familiar with where the center of your screen is without a reticle, you can progress to having no laser sight and blindly hip firing.
After practicing hip firing, start practicing your ADS or aim down sights. This is the final mechanic that you need to practice for your aim. Use an optic that you will actually use a lot of the time against real players.