I will add to this as I think of more but so far:
Follow the plans exactly - I saved some wood by not continuing the solid frame sides up higher to attach the temporary cross piece. This cost me lots of time, heartache and extra work in the long run as I had to buy more wood to support them higher.
Mark everything when on the drafting floor - some of the frames I missed the waterline and it was a pain to try and confirm them. It is also an opportunity for errors to occur.
Take your time with the frames - mine worked out fairly well and were level in each direction when they came off the floor. This makes it much easier when the time comes to line them all up, and it helps your confidence no end when things start to go right.
Measure twice, cut once - everyone knows this one, thankfully I only had to remake the solid wood for one frame.
Closely related is measure twice, screw once - as I was standing up the frames and moving them up and down each side I lost count of the times I had to remove screws because I had forgot to check something. Get it where you think it needs to be, then double check EVERYTHING before you screw it in place.
Standing up the frames - lots of clamps and take your time. Start with the centreline on the frame matching the centreline on the strongback. I used wire down the strongback for the centreline, then string and a weight to get the frame in the right spot. Use string from the centreline out to the sides of the frame to confirm they are at 90 degrees (the length of the string should be the same).
Keep your level close to hand - always keep checking levels in each direction. A little move one way can throw out other parts of the frame.
Don't forget to duck and lift your feet - as you move side to side and through the frames there are very hard pieces of wood at shin height and also some plywood stuff just at head height out of view. Trust me, it hurts!
Eat and Hydrate - keep water close at hand and drink often. Sounds simple but several times I got lost in the work and realised at the end of the day I was very thirsty. I also found sometimes I needed to walk away and have a break when things were not going well. Plus you get to look at what you have achieved so far which keeps the motivation up.