Perhaps you need to put a grain line marking on the pattern? I usually do this when I trace a pattern to make different sizes from the one purchases pattern. On manufactured patterns the grain line is thus: Then I write "straight of grain" or "grain line" between the two arrows. When you lay the pattern down on the fabric, you try to get the line between the arrows laid down directly on the lengthwise grain line of the fabric. Does this make sense?

Also, for pieces that are laid on the fold line you might want to make that marking too. Look at a manufactured pattern piece to see this marking - don't think I can make it with the keyboard.

You might want to mark notches or make a shallow cut into the seam allowance at the hip to match up the front and back correctly.

Be sure to mark your pattern pieces front, back, and right front, left front, right back, left back, etc.