I believe that the reason that you have not received any responses is that this really the kind of issue that varies with each individual. Let me see if I can help.
Infertility is defined as the inability to conceive after 1 year of unprotected sex. If you are asking about ways to increase "fertility" by this definition, then there are some options. However, if you are just asking about ways to increase your chances of getting pregnant, that is a slightly different issue. Really, the best thing to do, in either case, is probably to talk to your doctor. Your doctor will gather an appropriate history and assessment, and help you make a plan that works well for you. Pre-conception counseling is always helpful, even in situations where both partners are relatively "normal" in health.
Now, if a female just wants to learn about ways to increase her chances of becoming pregnant, I would recommend reading about:
1) the calendar method, 2) the cervical mucus method, and the 3) basal body temperature method.
All of these methods simply help to find the optimum time to engage in sexual activity.
Really though, for many reasons, the best thing to do is to talk to your doctor. I would make this recomendation for anybody. However, it is extremely important for you, because of your thyroid condition, not only to increase your chances of becoming pregnant, but to avoid any related complications. Also, regardless of the pregnancy issue, you need to know why you are irregular. This could be from your thyroid, your medication, or other issues that need to be considered (some of which may decrease your chances of becoming pregnant). Please, talk to your doctor.