This is largely the same goal that I've set for myself. I spend a good amount of time doing each (less marketing lately, more towards coding/design), and find

This is largely the same goal that I've set for myself. I spend a good amount of time doing each (less marketing lately, more towards coding/design), and find that while I outpace most people in these fields, there's always people who specialize even further and know way more about them than I do. The trick is to spend as much time learning from these people as you can. I talk with my direct superiors at work a lot, because they're both insanely knowledgeable engineers. I also have some buddies that do full-time marketing, copywriting, design, etc, and each of them are constantly teaching me things. Make a point to regularly associate with a wide variety of deeply specialized people, and as a result, while you'll probably never be as effective as any of them in their given fields, you'll certainly be way more effective than most people. From there, pick one or two fields to use as anchors for your T (or W) shape, and then leverage that in your dealings with other fields. Think of yourself as a pupa. Right now you're just incubating, you don't have to do anything fantastic, just learn and grow. Then, when you're ready, you'll break out of your shell and spread your wings :)