Light box
The simplest way to transfer your design to the fabric, is to trace it using a lightbox. Put the design page down on the lightbox and lay the fabric on top (you may want to tape them in place to stop them moving). The light will shine through and allow you to see the design well enough to trace it. It may still be difficult to see through very dark or thick fabrics, so in this case you may want to try one of the other methods below.
If you don't have a lightbox on hand, the same can be achieved by holding your work up against a window when it's bright and sunny out. But if you're doing a lot of transferring I definitely advise investing in a lightbox, it will make life easier! See the tutorial here
Special Interfacing
There are special kinds of interfacing you can use with embroidery to transfer a design. You can draw or print on the interfacing and then attach it to your fabric either by hooping them up together, or pinning the interfacing to the fabric. You stitch through both layers, following the design on the interfacing. Then when you're done you remove the interfacing. These special interfacings come in tear-away, cut-away and wash-away. But you do have to be careful to pull your stitches tight - they can often loosen up after the interfacing layer is removed.
Tissue Paper
Tissue paper can be used in a similar way to tear-away interfacing. Though I usually use large tacking stitches to plot the design out rather than stitch the finished piece. It tears away easier than the interfacing, though you may need a tweezers to remove all the tiny pieces.
Prick & Pounce
This method is another good one for transferring onto thicker and darker fabrics. Draw your design out on paper - I usually use thick tracing paper - and use a pin to poke holes along the design lines. Once all the holes have been pricked, lay the page on your fabric and rub the pounce (powder) over the top and it will transfer through the holes onto the fabric. Then you simply join the dots! This method is also very easy to remove if you make a mistake. You can get a prick and pounce kit from Sarah Homfray's website.
Printing
If those methods seem a bit too much trouble, you can always print your design directly onto the fabric. It may take a few goes to figure out how this best works with your printer, and you are limited to the size of page your printer takes. But it can be a handy technique to have under your belt. I have a tutorial for this method here, but basically you want to iron some freezer paper onto your fabric to help it feed through the printer. Alternatively you can pay a printing company - such as Pixalili - to print your designs for you!
Which way works best for you? Let me know in the comments!