When is the best time in a womans cycle to fall/get pregnant?

if the cycle is 28 day then it would be fourteenth day from last day
of period up to sixteenth day. But it is better to start from the
twelfth day as sperm can remain viable for longer time.

Based on normal cycles thatoccur every 28 o 30 days, ovulation
normally occurs between 11 to 19 days following the first day lf the
last menstrual period (lmp).  The best thing to do is monitor
ovulation, however if you have intercourse every other day during this
time frame, you will have maximized your efforts on achieving
pregnancy.  Here is a link on ovulation
http://www.americanpregnancy.org/gettingpregnant/understandingovulation.html
Here is an ovulation calendar to help you track you optimum days
http://www.americanpregnancy.org/gettingpregnant/ovulationcalendar.html
And if you have any success, here is a page to identify pregnancy symptoms
http://www.americanpregnancy.org/gettingpregnant/earlypregnancysymptoms.html

you count days in your cycle from day one = 1st day of your period, on
a 28 day cycle day 14 is mid cycle and is when most of us ovulate,
give or take a day, so this is the best day to have sex, sperm live in
your tubes for up to 7 days, but you should have sex on day 14 and day
16, then put a pillow under your backside for 30 mins so the sperm has
less chance of leaking out. on a longer cycle the time is counted 16
days to 14 days from the start day you are due your period, ie: a 34
day cycle would mean you ovulate between days 18 to 20  counting from
the 1st day of your period, so this is the best time for sex, to lead
to pregancy. for more information you can look up this site.
http://www.asksam2.com/femalesexuality/ovulation.php