Make any item of clothing that fits perfectly and looks exactly the way you want.

Supplies

Sewing Machine
Seam Ripper (or Scissors)

Materials

Fabric of your choice
Cardboard (or large sheets of paper such as packing paper)
Well-fitting clothing item that can be cut up (see step #1)

Step 1: Find a Well-Fitting Clothing Item

Find a well-fitting clothing item you're willing to cut up. This will be used to create the pattern for your new clothing.

Check your local thrift store for an item of clothing that fits well, but does not use a fabric with your desired color or style.

I found a pair of well-fitting shorts for $2.99 at my local thrift store.

Step 2: Disassemble the Clothing Item

Disassemble the clothing item into its original fabric pieces by using your seam ripper to cut the seams apart.

The easiest method for quickly cutting seams is as follows:

Turn the clothing item inside-out.
Use the sharp end of the seam ripper to cut a few stitches, enough that you can fit the dull side of the seam ripper into the seam.
Hold the seam taught. Insert the dull side of the seam ripper into the seam.
Slide the seam ripper along the edge of the fabric, taking care to cut only the stitching, not the fabric itself.

Cutting the seams of the rolled hems is optional. It can be time consuming, and it may be easier to simply add double the height of the hem to the new pattern piece.

Step 3: Create the Pattern

Identify the pieces of fabric that are symmetrical. Set aside one copy of the symmetrical fabric pieces such that each fabric piece remaining is a unique shape.

Create a pattern piece for each unique fabric piece:

Lay down each fabric piece on cardboard or paper, pinning or taping the fabric to hold it in place. Line up the longest straight line in the fabric piece with the side of the paper or cardboard if possible.
Trace around the edge of the fabric with a marker. Mark any places where rolled hem begins, or where other fabric pieces are attached.
Remove the fabric piece and cut the cardboard or paper along your traced outline.

Step 4: Cut Your Fabric

Take out your new fabric and lay it out flat with the "right" side facing up.

For each unique pattern piece:

Place your pattern piece upon the new fabric and trace around its edge with a marker or chalk.
If the pattern piece is used again symmetrically, flip over your pattern piece and trace around its edge again in an unused part of the fabric.
Cut the new fabric along the traced outline.

Step 5: Assemble the Clothing Item

Starting with two fabric pieces, align and pin the edges that will be sewn together with the "wrong" side of the fabric facing out.

Sew the aligned edge.

If the fabric is stretchy: use a zig-zag stitch. Otherwise use a straight stitch.

Place the sewing machine foot about 1 inch from the beginning of the edge.
Sew in reverse to the beginning of the edge.
Sew forwards, directly over the stitches you just made, to lock the stitch.
Continue sewing forwards to the end of the edge.
Sew in reverse, about 1 inch, directly over the stitches you just made, to lock the stitch again.

Repeat this for every seam of every piece of fabric.

Step 6: Rolled Hems & Elastic

If the original clothing item has any rolled hems, create them on the edges of your new clothing item.

To sew a rolled hem on an edge:

Fold the edge over once, roughly 1/2 inch
Fold the edge over again, another 1/2 inch
Sew along the inside edge of the fold, roughly 1/8 inch from the edge of the fold.

To insert any elastic into an edge:

Follow the same steps as the rolled hem, but with a piece of elastic inserted into the hem.

Place the elastic along the edge of the fabric.
Fold the edge over once, the width of the elastic
Fold the edge over again, the width of the elastic.
Sew along the inside edge of the fold, roughly 1/8 inch from the edge of the fold.