I used the hotel block link on wedding wire's computer site and it was ridiculously easy. Drury Inn blocked off enough rooms, extended the offer for an extra day, since our wedding is on Sunday and it's Valentine's day weekend, and we paid nothing up front. They gave us a deadline for guests to book and any unused rooms after the deadline just get opened back up to the public. Highly recommend.
Look for hotels that offer courtesy blocks. With courtesy blocks, you won't be held financially responsible for any room other than one you book for yourself, but the hotel still gives a group rate and holds a certain number of rooms. What I did was just call/email hotels that were within a short distance of our venue and then did a courtesy block with a Courtyard by Marriott near the venue. I was going to also do a cheaper one, but reviews online mentioned bed bugs so I was not going to direct my guests to that hotel.
I agree with the previous comments - look for courtesy blocks. You wouldn't be responsible for the costs of the rooms (guests can pay for their rooms when they reserve them), and they typically don't have a minimum number of rooms required for a courtesy block. Definitely check out the hotel room block tool on Wedding Wire, it's super easy to find hotels near your venue that would offer discounted rooms in a courtesy block.