Is their any certaing thing you canconcive a girl?

Not specificly. It is the swimmer (sperm) who gets there first that determines the sex of the baby. There is no special position, tea, day of the month or whatever else you heard that makes any difference.
No. There is not a way to be sure one conceives a girl. The only way to do that would be to select a "girl" sperm (carrying x chromosome) and not a "boy" sperm (carrying y chromosome). However, after conception, some of the embryo's or fetus's cells can be analyzed to see if it is a boy or girl. . . This can be done for families where all boys would have a bad disease, but where girls would be fine.