Advanced Font Manipulation
Changing Font Sizes
With the text selected, press
Ctrl+Shift+Comma(,) to decrease font size by 1 px and
Ctrl+Shift+Period(.) to increase font size by 1 px.

Kerning
Sometimes, two letters in typesetting have too much space or too little space between them. This is usually based on the shape of the letters. In the example below, the second one looks more aesthetically pleasing because of the decreased spacing between 'W' and 'i'.
Kerning adjusts the space between two characters. Photoshop has automatic kerning settings to help you do that: metric and optical. It's best to choose metrics if the font publisher made enough kern pair tables that manually adjusts the kerning between letter pairs. This usually means that metrics is a better choice if the font you're using is from a major type foundry or a reliable font maker.
If your font is from an amateur font creator, chances are it doesn't have a lot of kern pair tables (if it has them at all). That makes it best to choose optical and let Photoshop compute and decide for itself what the best-looking kerning is.
On top of that, it's also possible to adjust the kerning between two characters by putting the cursor between them and pressing
Alt+Left/Right. I usually don't do this for regular speech/narration/side-text fonts because of it's impracticality, but manual kerning adjustment is pretty useful for titles/covers and SFXs.

Tracking
While kerning is adjusting the space between two characters, tracking is adjusting the space in a whole selection (ex: a word, a line, a paragraph). I usually only use this for titles/covers and SFXs.

Baseline Shift
Adjusting the baseline shift means nudging individual character(s) up or down. Highlight the character(s) you want to nudge and use
Alt+Shift+Up/Down to move it.
By combining changes in font sizes, kerning, and baseline shifts, we can come up with an SFX like below. The first one shows the SFX without all the special manipulations, and the second one is the final product.


Horizontal Scaling
Sometimes, you'll come across a bubble that would look just perfect if that one line could be a little bit thinner. Like the start and end of the line are too close to the bubble borders, but that's the only way to make the whole bubble look good. Fear not! Just highlight the line and adjust the horizontal scaling from 97% to 103%. Any less or more than that, and the adjustment would be more noticable. Horizontal scaling is a better choice compared to tracking adjustment because tracking changes are more noticable.

Warping Text
Aside from manual manipulations, you can also warp the text instead. Either right click on the layer >> Warp Text or press
Ctrl+W to pop out the Warp Text window.

There are many different styles to choose from. Try and experiment to see which ones look good for which SFX. However, don't go overboard with the sliders and slide them all the way to the left or to the right. Most of the time, it'll just look unnaturally distorted and unreadable.
Using the Pen Tool
Google is your friend.