Joe,
Whenever you can, tak weld your work in AS MANY places as possible to reduce the "tweaking" or shrinkage. After correctly positioning and tak welding my work, I make several more "taks" about 1/2" to 1" long, essentially doing what George suggested. You can then proceed to weld in between without too much cooling time. The cooling time I use is equal to the duty cycle of my welder. 2 mins on...2 mins off, etc. Also to however long it takes me to knock off the slag and wire brush the other welds before connecting them all. Keep in mind, no matter what you do, those welds are creating stress and will move your work somewhat regardless.
When I started arcwelding again, I found it hard to gauge the "pooling" I needed for a super good looking weld without voids or porosity. It was easy when TIG welding and I always know when I got good penetration watching the "pooling" of both parent materials and the rod.
In arcwelding, I found by watching very closely and going slower I could see the "pooling" I was looking for. I also found that holding the rod more perpendicular to the bead(when possible) works better in shielding it than dragging it at an angle. The result are that I finally got not only strong welds, but porous free and good looking ones. I learned that making the best set-up I could (to the weld) was just as important as in TIG welding. I was able to use 6011 and 7018 to much satisfaction where they were harder to handle before.
The only thing I use 6013 for now is to cover up a big fat fillet after first welding with one of the others. I don't really like using it anymore becasue I can't visually see the pooling of the materials. In my case, the 6013 just seems to "roll over" the material, so I'm sticking with 6011 and 7018.
