I think all of our lessons are different, so I would have to know what you're doing to be able to advise you on what to continue and what's not as effective. But, you did ask me personally, so I'll tell you. Maybe it's just because I'm feeling inspired because I'm on a tropical business trip, but I'd say the biggest mistake I've made is putting TOO much emphasis on my work.
Follow up is the make or break of business relationships, so you can learn from that. I do a great job with following up with business contacts, however, when it comes to following up with personal relationships or taking the time out to vacation and see friends, I haven't done a good job at all.
The good news is, now that I see what I'm missing, I can change it. I've always taken relaxing spa-type vacations as opposed to coming back East to see my friends. I think we can mix the two. Once a year, plan a 4-day spa vacation (I can probably stay longer but they all have kids) so we can all see each other.
There is something SO special about being with old friends; reminiscing and sharing how everyone's lives have grown, the good the challenges... it's invaluable.
That's a mistake I made, and I plan to change it. You can learn from this, or you can apply it to your business by evaluating how you follow up with work friends/collegues.