I'm not getting sharp text, exporting to PDF

My document is a 24x30 poster that mimics a newspaper layout with several columns. It is essentially a collection of many, one paragraph, text snippets in Myriad, Regular, 9.5 pt, with paragraph titles in Myriad semi-bold, 10 pt.

Exporting to a PDF, High Quality Print, results in a file size about 250k. When a local copy/print store makes a laser print on regular generic paper, the text does not look all that crisp. So maybe it’s the paper? Or, the file size?

Previously, I had printed a similar, text-only, large PDF, created by Illustrator… and the file size was around 2.5 MB and the text looked good.

Once my final proofreading is done, I will have a final print made on better paper. But at $35 a pop, I wanted to be sure that I am doing everything correctly at the pre-press stage.

What settings are needed to have text printed optimally on a large poster?

*this is my first project with ID, but I am experienced with PS and AI.