Big decisions can be one of the most challenging parts of life, and to make good decisions, having a process can be very helpful. Thankfully, in his spirituality, St Ignatius created principles for decision making that have helped guide millions in making the right choice at the crossroads of their lives. This spiritual process for making decisions is often referred to as ‘discernment’, which means listening for the voice of God. Ultimately, if you invite God into this process, you can trust that He will guide you towards the right choice because He loves you and wants your happiness.
‘It should be as though at the centre of a pair of scales, ready to follow in any direction that I sense to be more to the glory and praise of God Our Lord and the salvation of my soul.’ St Ignatius of Loyola, Spiritual Exercises 
The first thing that St Ignatius says a person needs to do when approaching a decision is to become free from their attachment to any particular outcome. St Ignatius refers to this as indifference, which does not at all mean to become uninterested or cold to the outcome of the decision. What St Ignatius means by indifference is interior freedom. This freedom should allow you to be truly open to whatever God wants for you, even if this is not what you want. It can be very hard to truly shed your biases and step back from your desire for control, but it is certainly worth aiming to make your decision from this state of freedom, trusting that God wants what is best for you.
Once you find yourself at a good place, detached from a preferred outcome, it is then time to pray over the options, the different paths in front of you. Here, you want to listen for what God desires for you. St Ignatius believes that in following God’s invitation, you will have a feeling of peace and that this is the ultimate indicator that you are on the right path. Ignatius refers to this experience as ‘consolation’ and describes this experience in his Spiritual Exercises:
‘ ... I give the name ‘consolation’ to every increase of hope, faith and charity to all interior happiness that calls and attracts a person towards heavenly things and to the soul’s salvation, leaving the soul quiet and at peace in its Creator and Lord.’ St Ignatius of Loyola, Spiritual Exercises 
If you feel this way in your prayer, when considering one option, this would be an indicator that this is the right path to take. However, St Ignatius also writes about clear indicators of paths not to take, options that cause a person to feel the opposite of interior peace, what he calls ‘desolation’:
‘... ‘Desolation’ is the name I give to … darkness, disturbance in the soul, attraction towards what is low and of the earth, anxiety arising from various agitations and temptations. All this tends to a lack of confidence in which the soul is without hope and without love; one finds oneself thoroughly lazy, lukewarm, sad, and as though cut off from one’s Creator and Lord.’ St Ignatius of Loyola, Spiritual Exercises 
Essentially, this comes down to what is of God and what is not of God. In finding the choice God wants, you will experience peace.
Once you have made a decision, seek confirmation of that choice. This can come from the experience of consolation, from that sense of interior peace, or it can be found from outside yourself, in the words of those who know you well, or from testing that decision. Somewhere in these experiences, God can speak to you and give you a sense that you are going in the right direction.
Finally, just do it! Discernment should not be an endless loop of considering options, once the process has led you to your decision, you must act upon it. You will sometimes have to choose one good thing over another good thing but the aim is not the perfect decision, only the one that God wants you to make. Indecision is itself a choice that is generally a very draining experience. Whereas if you have achieved some level of interior freedom, considered and prayed over the options, and felt that decision confirmed, then you can step into that decision with confidence and trust that God is with you on your new path.
‘In every good election ‘decision’, in so far as it depends on us, the eye of our intention must be simple, looking only at what I have been created for, viz, the praise of God Our Lord and the salvation of my soul, and therefore whatever I choose must help me towards the end for which I have been created, and I must not make the end fit the means, but subordinate the means to the end.’