Patience is key to using construction lumber. Even if it says the lumber is kiln dried it will usually have a much higher moisture content then what is recommended for wood working. As the wood dries it will shrink creating internal stresses on the boards. Depending on the grain orientation this may cause the board to twist, bend, cup and or check.

To help combat the effects of the excess moisture you'll need to let it dry for a long time, more than a month most likely. You can help this a little bit by picking light boards (weight not color) since they have less water weight. Buying larger sizes also help because are not sold as often staying on the shelves longer drying out. 2X4s sell quickly so they are "fresher" and therefore have a higher water content.

Stack the lumber so that there is good air flow between the boards so they dry evenly.

Once the wood has had a good chance to dry you'll want to start cutting it to the rough shape.

You can see the effect of drying in the 2nd picture how the internal stresses in the board were released when it was ripped half. This may be due to there still being a higher moisture content in the middle of the board.

I found out the hard way I should have let these ripped boards dry some more before moving on, but I was able to make it work with a little more time on the jointer.