I took an early retirement a few years ago, this is good advice about cutting back work, but for many people it's hard to get there employer to agree to fewer hours. There are many reasons for this, not the least of which the way many employers control cost is buy just limiting headcount. Another option, which I took is to take a leave of absence. I took off 4 months, the most I could swing about 5 years before I finally quit. Certainly for 4 months I didn't feel bored at all. For me at least, two years now I'm not bored at all. For people interested in learning new technology, in my opinion there has never been a better time.

Also agree with the need to develop social connections outside of work. That could be friends you share a hobby or activity with, a volunteer group or cause you believe in, or anything else. Another option is finding part time work after you quit. I had a close childhood friend who asked me to help him with a project. We live in different parts of the country and previously we communicated at best once a year or so. Now even when there's not much to do we talk at least once a month.

I also recommend reading up on the subject before you do. This is reading list I went through leading up to my retirement. While much of the financial advice maybe out of date, some of it covers just the psychological aspects.

http://www.retireearlyhomepage.com/rebooks.html