Once you have a few patterns that you have sewn and have been adjusted for fit, you can mix and match parts of the pattern, much like changing the clothes on a paper doll. 

Just take care to trace waistlines, hip lines, bust lines and all lengthen and shorten lines - this will help you match different pattern pieces and ensure you don't end up with a jumpsuit which is too long or short. Just to be sure, check the length required by looping a measuring tape from front to back at mid-waist level and check the length along the seam of the pattern, allowing for seam allowances.

When you have the confidence or are simply frustrated with reigning in your creativity, there are a few things to bear in mind: 

Try to line up darts which cross the waistline, especially if you will trace the blocks out so they are not broken at the waist. You can turn the darts of the bodice and the darts on the waist to face each other, also, adjust the depth of the dart - by that I mean the circumference of the waist so that the bodice waist matches the skirt/trouser waists match and the darts cross the waistline from bust to hip in a straight line. Be careful to keep the original bust points in their original locations. Try make these changes on the paper pattern before you cut the fabric.

Carefully rotate the open ends of the darts - which will meet across the waist, so they face each other and can join in a straight line without twisting. 

A small alignment adjustment can be made, but try not to move the points of the darts too far over.

Drawing a centre line directly from the point of the bust to the end of the lower dart at the front, will allow you to press the dart crisp and flat once you've sewn it all together. 

If you are unsure, look at the darts on a dress which fits you for an indication of the shape and location of the dart. You can save a lot of time by borrowing elements that work on clothes you already have. 

If you are looking to change the sleeves on a garment or want to add your own there are also a few things to keep in mind. If the garment you are copying sleeves from has a tight sleeve, you may need to adjust the arm opening on the bodice if you want to add a loose-fitting sleeve. 

The same goes for a dress with a sleeve that is eased to fit the armhole - you will notice that the armhole will be the wrong size if you add a tight-fitting sleeve and there will be no ease.