One of the most important things to do is salat  (on
time).  After affirmation of faith, it is the most
important pillar of Islam.

Sahih Muslim, Book 001, Number 0151:  " It is narrated
on the authority of
'Abdullah b. Mas'ud that he observed. I asked the
Messenger of Allah (may
 peace be upon him) which deed was the best. He (the
Holy Prophet) replied: Prayer at its appointed hour. I
(again) said: Then what? He (the Holy Prophet)
replied: Kindness to the parents. ." The opposite,
abandoning prayers is disasterous for the hadith that
says  "What lies between a man and disbelief is the
abandonment of prayer. " [Muslim, Aboo Dawood,
Nasaa'ee] One should also develop a daily habit to
read the Quran.  Knowing the Quran allows one to
enjoin the good and forbid the evil. That is what
makes Muslims the best community. Quran 003.110  "Ye
are the best of peoples, evolved for mankind,
enjoining what is right, forbidding what is wrong, and
believing in Allah.".  Once you begin to learn more
about Islam learn about Dawah.  One good place to
start is Soundvision's good article on "Dawah in
public schools " (also click on the Dawah section in
this website).   However do not just talk about Islam
APPLY it to your life. Do not be like the donkey that
carries books on its back but benefits not by the
wisdom theirin (Quran 62:005).  Allah(swt) also says
Quran 061.003  "Grievously odious is it in the sight
of Allah that ye say that which ye do not."  One
should practice what one reads in the Quran and
Sunnah.  Be inspired by the feats of the Sahabah
(companions of the Prophet(pbuh)).  Read Companions of
the Prophet Vol 1-II by Abdul W.Hamid (very many were
young like yourselves when they began to struggle
mightly for Islam).  Surround yourself with the
company of the righteous.  Go to the ISNA and ICNA
annual conventions.   Choose your friends carefully.
There is a hadith that says one  will be on the deen
(religion) of his friend so look to whom you take as
companions.   Knowledge (in the Islamic sense)  is a
duty for every Muslim from cradle to grave (and
knowledge of one's deen is the highest form of
knowledge).  Associate with knowledgeable Muslims.
Start a  Halaqa (study circle) in your MSA if there is
none. Finally, last but not least, use your youth  to
memorize the Quran. Time is a powerful notion -- use
it to your benefit. Remember the golden years of
memorization are from 5 -23. Many great Muslims
memorized the  Quran under the age of ten.
Memorization gets more difficult with advancing age.
(Of course, while memorizing becomes more difficult
with advancing age,  wisdom becomes easier). There is
much reward in this activity.  Tirmidhi, Ahmed, Ibn
majah, and Abu Dawud, recorded that the Prophet  (saw)
said "It will be said to the companion of the Qur'an
on the Day of  Judgment, 'Recite and ascend (in
Paradise), recite slowly (or with tajweed)  as you
used to do in your earthly life, for your place (or
station in  Paradise)  will be where (you are when)
the last verse of your recitation ends."  What a
tremendous reward !!!!! How generous is our Rabb!!
Look for lessons at your local Islamic Center.  (For
those of you interested in attending an Islamic
University -- you should know that some have three
important prerequites for admission (1) knowing Arabic
(2) having memorized at least one juz (1/30th ) of the
Quran. & (3) daily prayers )

And Allah (swt) knows best.