As we grow older in the family of God, our enemies aren't just our own fleshly lust nor worldly system but also the devil.

Therefore it is important to always be ready to resist him.

It is not that easy though...
The bible states in,

James 4:7
Submit yourselves
therefore to God.
Resist the devil, and
he will flee from you.

It is therefore imperative to always be under submission to God.... to be under his power.

Only then can we resist the devil...Only then will he flee from us...

Take note that we are always on a constant spiritual battle.

As a young adult, think of yourself as a soldier of God and keep the following verses in mind.

(Ephesians 6:10)
Finally, my brethren,
be strong in the Lord, and
in the power of his might.

Your main source of strength is God. Defend yourself by the power of God's might. 

(Ephesians 6:11)

Put on the whole
armour of God,
that ye may be able to stand against the
wiles of the devil.

Our enemies are not the people around us. So the battle is even more dangerous.

(Ephesians 6:12)
For we wrestle not
against flesh and blood,
but against principalities,
against powers,
against the rulers of the
darkness of this world,
against spiritual
wickedness in high places.

During the battle, always wear the proper armor. Hence, you should always be wearing not only SOME armor but the WHOLE armor of God.

(Ephesians 6:13-17)

Wherefore take unto you
the whole armour of God,
that ye may be able to
withstand in the evil day,
and having done all,
to stand.

Stand therefore,
having your loins
girt about with truth, and
having on the breastplate of righteousness;

And your feet shod
with the preparation
of the gospel of peace;

Above all,
taking the shield of faith,
wherewith ye shall be able
to quench all the fiery
darts of the wicked.

And take the
helmet of salvation, and
the sword of the Spirit,
which is the word of God:

Our enemy is not an ordinary being too. Hence we should always be connected to God by calling him always.

(Ephesians 6:18)

Praying always with all
prayer and supplication
in the Spirit, and
watching thereunto with
all perseverance and
supplication for all saints;

Here is a big  NO
in fighting your battles:

Don't be a LONE ranger!

Stay with God all the time, and stay also with other children of God to help you with your battles.

Fear not!
for God will
never leave you
nor forsake you!

He promised in:

(Isaiah 41:10)
Fear not;
for I am with you:
be not dismayed;
for I am your God:
I will strengthen you;
yea, I will help you;
yea, I will uphold you
with the right hand
of my righteousness.