In Smash 4 there is a six minute timer for each match. One way you can win is to get that timer to zero and have more stocks and/or less percent than your opponent. Some people treat timeouts as somehow a lesser victory than KOing your opponent but you should do your best to rid yourself of that notion. If you are playing to win and timeouts are wins, then you need to practice for timeouts!
In order to start being comfortable with timeouts, understand that time is a lot like percent in smash, it exerts a pressure on your opponent (and yourself) and must be respected. When percent is getting high a player has to start respecting new options from their opponent, like killing moves. Likewise, when time is running low certain strategies become more viable that normally would be considered subpar. Each player will react differently to this change in game tone, so understand each opponent’s habits when timeouts are possible. Some may attempt to time you out back; others may double up on aggression. Even if the game doesn’t end in a timeout, exerting the pressure of the clock can lead to your victory.
Since many players have little respect for timeouts they become more agitated and can quickly become tilted if a timeout is pushed. This all by itself could be your key to victory, as a tilted player can become much easier to read. (Careful of players who can seem to play even harder when you push their buttons.) If you as a player are known for being comfortable or even relishing in the thought of timeouts, this can make a player feel defeated before they even start.
Go into the lab and practice timing out. Do it in friendlies. Have yourself and a friend both practice timeouts on each other. Matches will be about establishing a lead and holding on to it, which at first may be really boring and not fun at all. In fact, the less fun you have the more necessary the training probably is, since people generally hate training at things they are bad at or that they hate their opponents doing.
Remember, this is Smash. The only rules during a match are win and don’t punch your opponent in the face, basically. You can only gain from being comfortable with different types of wins.
Get to work!