Sins quiver a heart - Ibn Mas'ud
In reality, there's a fine line between sins and goodness. We all stand on that fine line, either quite rigidly, slightly tilted towards either two or had completely picked a side. To be truthful, that line is so blurry and faded for our physical eyes that looking down, you won't know where you stand at all.
True, unless you had it in you (piousness, knowledge and bright mind), this line wouldn't be much of a line but only a plain, road with no pavement and no traffic. You'd wonder around, aimlessly, as if your eyes are blinded by a strong and transparent cloth, which held over you and was to never let go.
Piousness is when you have that belief and clear commitment towards the creator; Allah. Knowledge is when you get to know Islam, the Prophet, Allah and etc in great depth. You flick through and look back at the pain and the joy of the Muslims before you, their unyielding grip towards their religion and the strong tribulations some have faced. So, along with a bright mind (healthy and free from any negative captives of today's world), you'd woke up and see the fine line.
Now that you see the line, how do you know when to jump, dodge or run? We have our hearts for that. A box of emotions, blood pumping mechanism and an oxygen provider as to keep us alive, our hearts does so much than that. It is our counselor and an expert in you, us and me. Allah have made this a medium as to how He could provide you a sign and answers. So whenever you're facing the biggest decision of your life, perform an Istikharah prayer and ask Him what's best for you. Then, place your hand on your chest and ask your heart what He'd instill in it.
Even on the smallest of matter; when you're confused or you're stuck in a 'syubhah' matter, consult your heart.
On the authority of Wabisah Bin Ma'bad R.A, who said;
I came to the Messenger of Allah P.B.U.H and he said, "You've come to ask about righteousness". i said, "Yes". He said, "Consult your heart. Righteousness is that about which the soul feels at ease and the heart feels tranquil. And wrongdoing is that which wavers in the sould and causes uneasiness in the breast, even though people have repeatedly given their legal opinion (in its favour)".
As what the Prophet Adam A.S had decreed, amongst three are:
1) Repress yourself from doing something which your heart feels unease at.
My heart was trembling the moment I was about to eat the fruit from the forbidden tree.
2) Imagine how it'll ends or what will arise if you were to carry out the act.
If only I know what eating the fruit would've caused me, I wouldn't have even touched it.
3) Consult other people.
If I'd been consulting the angels first before eating the fruit, they would have told me not to.
An act that will benefit yourself, as well as others (humans, other creation of Allah and etc). For example, good deeds towards one's parent.
An act as a prove of your loyalty towards Allah S.W.T for surely, being loyal towards Him, His command and forgetting His forbiddance is the most tangible and utmost goodness.
Characteristics of one's heart whenever you're about to approach a wrongdoing or a sin is that you'll feel unease, nervous, worried, cautious, scared and you'll wnat to hide your action from the eyes and knowledge of others.
So, consult your heart. May we'll be given a clear guide as to how we could navigate.
Allah knows best.