Strategies on flanking enemies as Scout

A golden rule to follow as Scout, and any other flanking class, is as follows: don't follow your team*. As a Scout, you rely on the element of surprise for most of your kills, so try to stay away from whatever path your team is taking at all costs. This will also help you avoid the main front of the enemy attack, since most frontline classes like to take the same route.

If you do happen to run into an enemy face-to-face, run away. You can outrun any class besides another scout** by backpedaling, so take some shots while backpedaling, duck behind a corner, and take another route (or double back once you've lost them). You perform much better when you get the drop on someone else.

Also learn to make good use of your mobility. Different loadouts will offer you different mobility options. The BONK! allows you to move with impunity in dangerous situations, the Winger lets you jump higher and double-jump higher, the Atomizer gives you an extra double jump at the cost of some health, the FaN gives you an extra jump, and the Soda Popper gives you lots of extra jumps. These all help you avoid damage, and help you reach locations others can't for ambushes and flanking potential.

The Baby Face's Blaster can also improve your mobility, but rather than giving you extra jumps, it allows you to move faster as you do more damage, at the cost of having a lower base speed and losing half your extra speed when you double-jump. This requires you to be very conservative with double-jumps, and requires you to do some base damage to start, but can be very, very effective once you've gotten familiar with both the class and the map you're playing on.

One last important tip for playing Scout - know where sentries are going to be placed. If you haven't played a map before, be careful going around a corner because there might be a sentry, and it will wreck you. BONK! can help avoid some damage, and get you to places where you can flank, but you should still be incredibly cautious of sentries, as there is little you can do and they will happily tear you apart in seconds even at the lowest build level.

*And teammates? Do the spies, pyros, and scouts a favor - don't follow us. We rely on stealth, and we won't get any of that if we're being followed.
**Or a charging Demoman.