The great thing with silk is that it is far more wrinkle-resistant than cotton and also recovers more quickly from wrinkles. Of course, some wrinkles will always have to be taken care of with an iron.
When ironing a bow tie for the first time always start with the neckband. This area is not seen when worn so it is a great place to try out your technique without ruining the bow tie. Also, this way you can test if the fabric dye will run. If new to ironing please practice with some older bow ties before moving on to your favorite tie!
On most printed bow ties(ones where the design is printed onto the finished silk) you can use a fairly hot iron with steam. Try not to press too hard and let the steam do most of the work. On repps and most wovens(thread is dyed and pattern is woven into finished silk) turn the steam off and just use a hot iron. As with the printed bow ties try not to press too hard and let the heat do the work. With all bow ties start with the least amount of pressure that will get the job done, only increasing pressure if needed. If ironing anything with man made fibers such as polyester turn the heat way down since you can actually melt the fibers!
The last piece of advice also pertains to suits and that is be very careful with darker colors, especially navy, since hard pressing can leave a sheen on the fabric. With darker fabrics I would recommend lifting the iron slightly away from the fabric and using just the steam to relax the fibers. Usually this will remove the vast majority of the wrinkles. If steam alone does not do the trick then take a clean hankerchief, t-shirt or any other white piece of cloth and place it over the bow tie you are going to iron. This extra layer prevents sheen and lets you press as hard as you want since the fabric layer acts as a buffer between the iron and bow tie.
Hope this was informative and please email me firstname.lastname@example.org if you have any helpful tips of your own.