Age : Age is inversely proportional to fertility. In both men and women, with the increase in the age, fertility decreases. The fertility is at its peak from 20-30 years of age and gradually decreases post that.
Alcohol : Smaller or larger the dosage, alcohol plays it's role adversely in conception and pregnancy. From causing birth defects in the foetus to decreased sperm count; the consumption must be stopped whenever pregnancy/planning is involved. Read the following article for further information - http://community.askgargi.com/339/alcohol-a-major-hindrance-to-fertility-and-conception
Smoking : Active or passive, smoking causes irreversible genetic damage, lower quality sperms etc. in men. While, in women it results in miscarriages. The following article discusses in details the impediments smoking causes to fertility - http://community.askgargi.com/333/smoking-an-impedient-to-conception-and-fertility
Occupational hazards : Be it radiation, heat, chemicals or fumes; these directly affect the fertility by reducing sperm count in males.
Emotional health : Conditions like depression which tweak the hormonal levels tend to affect ovulation and sperm motility/vitality. It is suggested that, one should refrain from using antidepressants from at least 6 months before planning for a baby.
Weight : An average/optimal Body Mass Index is preferable for fertility. Check this to understand why BMI matters.