From Subversive Cross Stitch:
FIRST, make SURE you have separated the six-strand embroidery thread and you are stitching with only TWO strands. SUPER IMPORTANT!!
Embroidery hoop: You'll need an embroidery hoop to hold the fabric taut while you stitch. Believe me, it just doesn't work without one. It doesn't matter what material it's made of - plastic, wood, whatever. Just make sure the hoop clamps the material all the way around.
To Begin: Find the approximate center of the pattern. Then, find the approximate center of your fabric. Begin stitching something that's near the center of the pattern. Working this way (from the center out) will ensure that you don't stitch right off the material.
The stitch: Our patterns are very simple and almost always require only the basic "X" stitch. If your pattern has any straight lines in the design - stitch those exactly as they are on the chart. Remember, cross stitch is a lot like connect the dots!
To begin stitching, bring the threaded needle up from the back of the fabric leaving about a 1" tail of thread behind the fabric. Stitch the next 5 or 6 stitches over the tail. Clip off extra thread. To end off, weave your needle back through the last 5 or 6 stitches and clip the thread short so as not to leave a loose tail. Alternate method: You could also just make a knot if it's easier for you, just make sure the knot isn't too big and lumpy.
Figure 1
Stitching Tips: There are two methods. The first method is to work a row of half stitches (////), then work back (\\\\) to complete the "X"s (Figure 1). Use this method for most stitching. The second method is to complete each X as you go (Figure 2). Use this method for vertical rows of stitches. The main thing is that each "X" crosses in the same direction. That is, the top thread of the "X" should always slant in the same direction (either \ or /). It doesn't matter which way they slant, but if they're mixed the finished piece will look uneven. Remember to relax as you stitch. Your stitches should lie flat on your fabric and not distort the holes or the fabric.
Changing Colors: Sometimes a color will have only a few stitches and then "jump" to another area. Most of the time you should end off and start again, other times you can carry the thread along the back. Be aware that sometimes the thread will show through the white fabric. Finishing: It's a good idea to wash the finished piece. Just hand wash it in some cold water with Woolite or very diluted detergent. Let it dry fully, then press with an iron. I'm kind of informal about these things, just be careful not to burn the final product! If it scorches, it will wash out. A scorch looks like a light burn. Like toast. (Mmmm, toast. Not good in this instance, though.) Try to wash it out, you'll be surprised.