It's not easy. Truth is, it kind of sucks at first, until you learn how to do it. But, once you get it into a formula, it's mostly a matter of creating the proper mechanics, finding (and cropping) the right art, and producing the whole enchilada.
If you're new to making professional-looking homebrew, I'll break it into three steps:
- First, required reading. Read The Mousefolk Guide by reddit's /u/skybug12. It tells you the general ins and outs of how to do things in the PHB style, requiring only light-moderate Photoshop knowledge and some serious patience.
- Be sure to download the brushes, fonts, and other miscellaneous materials that /u/skybug12 includes as part of his guide. These are especially important - you cannot duplicate the PHB style without this pack.
- Lastly, to make it even easier and to get access to elements of the pack above, be sure to download the template that I use to make everything here. Included in this template are:
- Text columns and headers complete with formatting
- Graphical element for the Optional Rule sidebar block
- Graphical element for the Expanded Spell List
- Graphical text element for the Monster Stat Block
- Example pictures for picture elements on the page, to give a general idea as to how they're done.
Sounds simple, but is actually a massive pain in the butt to generate in the first place (especially the monster stat block, hoooooly fuck was that hard). Feel free to use the template for your own content, just be sure to credit me when you use it, same as I credit /u/skybug12 in my homebrew.