A balanced diet should provide all the nutrients you need. It is advised though to take a supplement of Folic Acid (400 micrograms per day) for 12 weeks before you start trying for a baby to help minimise birth defects such as spina bifida. 

There are pre-pregnancy supplements available which some women choose to take to ensure they are not deficient in any vitamins or minerals. It is not advisable to take any non-pregnancy supplements while trying for a baby as these may not be appropriately formulated and can contain ingredients not recommended at this time.  For women with a BMI over 30 (check your BMI range here) it is advised that a higher folic acid supplementation is taken of 5mg (milligrams) per day. If this applies to you, if you have a family history of spina bifida or you take anti epilepsy medicines your GP will be able to provide you with a prescription for the high dose version.

Don't forget the man in your life - get him in shape too...