Fees cause the biggest problems for employers. The majority of plan litigation is about plan fees. Be informed. 

Still somewhat new to the 401K world and significantly different from the better known Roth IRA. Roth 401K is a better option. 

Most employers don't realize the liability surrounding hardship distributions nor what their responsibilities are.

There is still a lot of confusion regarding deposits. Different rules for employer money vs. employee money  and correction is complicated.

Every plan requires corrections to be made at some point. There are very specific rules regarding the proper procedure for correcting plan failures. 

Automatic enrollment is a terrific way to improve plan participation. But be careful, the rules surrounding it can be daunting and may deter you.