It is not necessary to use all 3 methods.
Most women use Basal Body Temperature and cervical fluids.
You may have other signs of ovulation as well. These may include mittelschmirtz
(a pain on one side of the abdomen caused by the follicle rupturing
and releasing the egg), breast tenderness, increased libido.
Some women will find these to be highly accurate indications of ovulation,
while others will not experience them at all.
Take your temperature upon waking, before any other activity, after
at least 3 hours of sleep. Use either a digital thermometer or a special
BBT thermometer (makes it visually easier to read the decimal points).
Be consistent as to what time you take your BBT and where you take
it (either orally or vaginally).
Once you have completed a chart you can tell by looking back you can
tell when/if you ovulated. You will not be able to use temperature
for ovulation prediction.
Once ovulation occurs progesterone causes a rise in your body temperature,
so you will know that you have ovulated.
If the egg is fertilised your temperature will continue to rise for
18 consecutive days, if not the day before your period begins will
have a drop in your temperature.

Your cervical fluid will change throughout your menstrual cycle. By
observing and recording these you will know when you are probably
fertile.
During menstruation you will have very little or no noticeable cervical
fluid (Dry). Following menstruation, the fluid will become sticky
and then possibly creamy and white. As you near ovulation, your cervical
fluid will become clear, stretchy, and resemble raw eggwhites. The
last day of egg white is your most fertile time.
This is your most fertile time. The "eggwhite" fluids enable
the sperm to survive and swim towards the egg. Following ovulation
your cervical fluid will change again.
The
cervix is located at the top of the vagina. You can reach in with
your finger and judge the height, softness, and the size of the opening.
Always test it in the same way, either sitting on the toilet or squatting.
Approaching ovulation - your cervix will rise (so that it is harder
to reach), soften, and the opening will widen. After ovulation - your
cervix becomes lower and begins to harden again.