If you're in a squad, you need enough loot for 3-4 people. This means you are going to have to jump towards a high loot area or risk being undergeared by the time you engage someone. As a solo player, you can take advantage of this knowing that some of the smaller villages will be relatively unpopulated at the beginning of the game.

Which brings me to my second point - as the game goes on, people will die and the average size of each squad will be reduced. If you can avoid fighting other players until there are 25-50 other players left alive, you will greatly reduce the odds of a 1v4, although it's still a possibility. During a top 10 situation, it's more likely you will be fighting against teams of 1-2 players, but the possibility of a squad making the top 10 intact does exist.

It's not always possible to avoid a fight. If you do have to fight, there are a few strategies you can employ. First, if you have the advantage of surprise, your initial attack could take out 1-2 members of their team and even the odds for you. This isn't always the case though.

When possible, try to find an area with a bottleneck. The stairwells inside the 3 floor building in the military crater area are pretty good for this - provided you know nobody is above you in the building, you can 3rd person from around the corner and wait for the enemy to try and push you. There are other buildings with choke points like this too. The bottom line is - you are much safer with your back to a wall, but watch out for grenades. Some buildings do have bars on the windows to prevent this - try to use those rooms with the barred windows if you are holed up in a house versus a squad.

If you are caught out in the open, you may be screwed. If you have solid cover, such as a rock, you do have a chance. Just 3rd person the rock and wait for them to try to flank your 3 'o' clock or 9 'o' clock and pick them off as they do so. Make sure to vary your shooting position each time you pop out, i.e. first pop out to the left, then pop out to the right.

Finally, if you are fighting them in a city - one option is to shoot, then fall back to a different cover. Your enemies will typically approach you at different speeds due to their original distance. When you run, fight, and run like that, you can effectively make it a 1v1 fight several times instead of a 1v4.