I want to preface this by saying that these are not all the possible things that can help with speed, mostly just beginner info, and they may change in later patches.

1. Alternating attacking and blocking in quick succession allows for more possible hits since you do not have to go through with the entire swing. This is mostly useful against large, immobile bosses. Your character will always start swinging from their left.

2. Portal as much as you can. It not only saves huge amounts of travel time, especially considering not having to use energy to dash when you portal places.

3. Make a portal to Santa Fae before entering the Winter fight. This lets you quickly go back to Santa Fae after the fight, but you cannot open a portal after the fight.

4. Know when to shop. Gold can be a bit light in the run until Tai Ming, but slight damage increases can help a lot.

5. Picking up any item that gets held above the character's head, that animation can be cancelled by blocking while getting the item (keys, baking soda).

6. (Multiplayer only) Video link (not mine) provided here for explanation: Instead of entering the map on the left side, enter on the right. This skips the Hydra boss and a lot of the temple. Winter mode must be enabled to move the vine so the out of bounds player can re-enter the map and open the way for the in bounds player.