There's a joke, "How hard can it be not to install wires?" However, it's a good question, so let's think through this a bit.
Let's say you are deploying a new wireless network. Maybe you had it thrown at you already purchased and delivered. You just get to implement it. What fun! Maybe it's "just" an upgrade, so can't you just swap things out?
Things you need to consider: What model are the APs? Do you have enough for coverage? More importantly, what about capacity? If not, you may have to pick and choose the most important locations to get quality wireless and accept lower quality wireless at less critical spots. Maybe it's a network designed for 2.4GHz radios and you are upgrading with the expectation of 5GHz coverage. 5GHz needs more radios to achieve the same coverage, so a simple swap might not do the job. Especially if it's a 2.4GHz network that was focussed only on coverage.
Instant or controllers? Do you have multiple controllers for high availability? What happens when a controller goes down? If it's not too late, is the controller the right size for this deployment? Not long ago, I was giving some advice to a friend who had a pallet of gear handed to him and told to deploy it. Among other things, it included a single controller that was overkill for the deployment, when for less money a pair of smaller controllers would have been a better plan. We want to avoid these kinds of problems when we can, but make the best of them when we must…
So, funny thing about wireless is it still needs wires. Doesn't matter where the best place to locate the AP is if you can't run a cable there or the run is too long. Perhaps it turns out the architect of the building moonlights as a wireless engineer and there are helpful "WAP" locations spread around the building. Or maybe a wiring contractor was brought in and they expressed their RF design opinion with some random cable runs for you. Usually too many, sometimes too few, and almost always not in the right place. Ideally we get the cables where we really need them, but again sometimes we must make the best of things…
You also need a place to connect that cable. You may need more switches or an upgrade to the existing switches. Are there open ports? Are the switches PoE? Do they have the PoE budget to support the APs you are adding? Do the switches support 802.3af (15.4W max) or 802.3at (30W max)? Better make sure the APs don't require more power than you have available. Now that you are adding load to your switch, do you have the capacity on your UPS to support this additional load? That's probably not a problem, but it's worth checking.
Do you have sufficient bandwidth in the uplinks to support the requirements? What about in a year or two? Consider how the network may change in the next few years and whether it will be able to continue to meet expectations. For example, I've been designing everything for 5GHz for the last several years, even though there was no real demand for it until about a year ago. Given the explosion of 802.11ac devices, I'm very glad I did even though many of those deployments are still only 802.11n. Those 802.11ac devices are making use of that 5GHz spectrum, adding capacity for everyone.
How are clients going to authenticate? Open network, username/password, PSK, certificates? Do all the clients support your authentication protocol? Does the infrastructure actually support it? It's great to say everything will get an X.509 certificate to authenticate, but does the required PKI infrastructure already exist? If a directory like Active Directory is already there, it probably does. Pushing out certificates to AD domain joined machines isn't difficult, but is it ready for BYOD? Now you're looking at something like ClearPass to help manage the on-boarding process.
How many SSIDs will you need? Do you need multiple classes of users on the same SSID? How will they be named so users can easily determine the correct SSID? Have you considered an authentication system that can assign users on the same SSID to different VLANs to simplify the interface for your users?
Is there a guest network? Will it have a captive portal? Who's building that web page? Is it a static page or dynamic? What serves the portal pages? Do guests need to accept an AUP? Will you limit speeds or connection time? Do your guests need sponsorship? Depending on what is needed, the complexity can grow very quickly…
How hard is it not to deploy wires? That depends on whether you planned it before the deployment or during the deployment. A modern wireless deployment isn't simple, but planning all these things well in advance will make it a lot easier. There's plenty not covered here, but the idea is to get you started thinking about all the details before they have a chance to bite you. If I missed your favorite pre-deployment checklist items, please leave a comment!