The answer to that is that, compared with a lot of people, the plans I get down on paper are actually quite sketchy. I also wrote Searching without reference to any sort of plan (hence the slightly curious double bite ending and a couple of other issues. Suffice it to say that I planned Witch Hunt rather more thoroughly. And then largely ignored the plan of course, but still...)
- The first key to better pantsing is simple: recognise that you do actually have a plan. It just happens to be in your head. Almost no one writes with no overall idea of where they are going and what they want to happen except possibly as some sort of deliberate experiment. Even if you don't want to write it down, take the time to fix it clearly in your mind's eye before you begin.
- Keep notes. One of the major problems to affect this sort of writing is the continuity error, so make sure you keep track of what is going on.
- Learn about novel structure. Good structure is important if you're going to come up with something that is balanced, moves forward well, and comes to a pleasing finish. Even if you aren't going to meticulously plot your architecture, it still helps if you know what it should look like.
- Be prepared for a total rewrite or two. Of course, this is true of all novels, but I find that well plotted ones need it less. The base there is sound. It's the execution that is a problem. Pantsed novels often have deeper flaws that need big changes to correct. What I'm saying is that this is not some 'easy' way to do the work.
- Recognise the limits of your inspiration. It may be that you get a chapter or two in that first burst that you absolutely have to get down in one go. Just because you've started that way though, don't be afraid to admit that you have reached the point where the inspiration has run out, stop, and take a moment to plan your next steps.