Brakesliding is a precise form of movement that can be performed out of a skid. With rolling speed, an optimal brakeslide starts at -23 speed, slowly decreasing to 0. For comparison, a roll is 26 speed.
Since a brakeslide is slower than a roll, it should only be performed in instances where you still have some distance to cross, but not enough place to do a roll. A good exemple of a place where it can save time are inside dungeons, when you want to reach a door but are in a position that would cause you to bonk if you do a roll. Doing a brakeslide instead of walking usually saves 2 or 3 frames in those circomstances. Brakeslides can however end up being faster than roll when going up slopes, because slopes alter positive speed movement options significantly.
Due to how precise the timing for an optimal brakeslide is and how little time it saves, it is usually not used in real time runs.
This trick abuses something called the ESS position. ESS stands for Extended SuperSlide Position, it is smallest input of the control stick that the game registers as not being in the deadzone. In particular, this trick mostly uses ESS Down, which is the closest your joystick can be to neutral while being below neutral, and the game considering you not neutral. But all 8 cardinal ESS directions are useful especially if the camera is not directly behind Link.
The picture below shows the shape of the deadzone in The Wind Waker. It is a square except for the trimmed four corners. Thus, while stick values 110 and 146 usually corresponds to a perfect ESS, the perfect diagonal ESS positions have stick values of 111 and 145.
To perform a Brakeslide, you must initiate a skid while holding target. To do so, move forward then input L+down. You can avoid entering the skid animation by switching to ESS Down or L+ESS Down on the very next frame. Your will keep almost all the speed you had, but it will turn negative. Keep holding ESS Down to slide at that speed, slowly decreasing.
Brakesliding is usually performed out of a roll in order to brakeslide at rolling speed. To do so, perform a roll and press L+Down on the first frame after the roll animation ends. Then on the very next frame hold ESS Down or L+ESS Down. You will be sliding at -23 speed, slowly decreasing.
Holding L+ESS Down will allow you to keep sliding while facing forward, which can be useful if you need to perform an action such as opening a door or a chest, or climbing a ladder. Instead of holding L, you can also mash the L button perfectly to conserve slightly more speed than by holding L. If you only hold ESS Down, Link will turn around and face backwards, but you will retain your speed better. If your down input was perfect relative to the camera, Link will perform an instant turnaround. If it was not, Link will turn around slower. The direction Link turns around depends on the angle of the skid input relative to Link's facing direction. If the down input is to the right, Link's feet will shift to the right at the beginning of the brakeslide and Link will turn around facing left. If the down input is to the left, Link's feet will shift to the left at the beginning of the brakeslide and Link will turn around facing right.
After initiating a brakeslide, you can decide to make Link face sideways by doing the following inputs: ESS Down -> ESS Down-Right -> ESS Right, or ESS Down -> ESS Down-Left -> ESS Left. This is the best way to conserve your speed during a brakeslide. Whether you're able to face right or left depends on the initial down input like noted above, unless you held L one more frame than necessary, in which case you can choose to turn right or left.
Managing Link's facing direction is a complex task and heavily depends on the camera position. It is possible to perform a brakeslide facing forward without holding or spamming L by performing complex ESS changes every frame. This only really saves time for very long brakeslides however.
There are also ways to start a brakeslide with almost the full -26 speed (instead of the usual -23) but they require some specific situations. Performing a brakeslide out of targetting an enemy allows a -26 speed brakeslide (L must be released early enough for the untarget to occur on the right frame). With a first person item equipped, it is also possible to start -26 speed brakeslides but these will shoot Link perpendicularly to the initial roll direction. With the grappling hook or the bow (which shoot Link to the right), roll then hold ESS left. Press the grapple/bow and L on the first frame the roll ends, hold L one more frame then release L to have a perfect speed brakeslide towards the left of the initial roll direction. With the hookshot, the inputs are mirrored.
When a first person item is equipped, it also becomes possible to change your momentum direction while in an extended brakeslide with no speed loss. To do so, pull out item and target on a specific frame while in an extended breakslide. Pulling out the grappling hook, boomerang or bow makes you go to the right. The hookshot makes you go to the left.