hi, as you are trying since 2 yrs you are fit in defination of infertility, so first consult infertility specialist, sm investigations for you and your wife is mandatory at this stage and if all investigations are normal start basic treatment like ovulation induction which will increase your percentage of conception double than normal sexual relation
Age, frequency of intercourse, general health & few gynaecological problems or male fertility issues, can have an impact on the ability of a coulple to conceive.
You should ideally have regular intercourse at least three to four times a week, and not try to stick to any particular time of the menstrual cycle.
The chances of conceiving are maximum between 12th to 16th day of the cycle, assuming your wife has a 30 day menstrual cycle.
A healthy lifestyle is important. Good diet, appropriate rest & exercise, maintaining a normal body weight, avoidance of smoking and drinking would be helpful.
If your wife has any current gynaecological problems like irregular periods etc, or if you have any current health problems, you should see a gynaecologist soon, as it has been two years since you have been trying.
I would also advise your wife to start taking folic acid tablets from now itself.