A low consumable cost will ensure you aren't paying an arm and a leg every time your printer requires new toners or drums.
Adequate print resolution
Print resolution is mostly important when printing graphics. Take resolution into account when considering how you will be using the printer. If you need the utmost text accuracy, consider a higher-end monochrome laser printer with lpi (line per inch) quality settings.
Low power consumption
Laser printers can be much more power-hungy than a desktop PC, particularly if constantly printing. Look for a model with energy-saving modes and Energy Star certification.
Adequate operating system support
Check to see that your laser printer will be compatible with the operating system (or systems) used in your office. If driver support isn't included, ensure that the printer has an adequate emulation language so you can still print and control its functions.
For older computers, you may still need a parallel port connection, though in most circumstances you will only need a USB 2.0 connection for local printing. If you want to network the printer, however, ensure it has an Ethernet port or integrated Wi-Fi.
A laser printer with 32 or 64MB of RAM may not cut it out for a workgroup of five to 10 people who need to print regularly. You don't necessarily need to buy a printer with loads of memory from the get go, but ensure you can at least upgrade the memory later on if you need to.
Suitable accessories and paper handling
Ensure the laser printer can handle your paper requirements, such as A3 media or envelopes. Also look for accessories that can cut consumable costs, like an automatic duplexer.