In an earlier post, I suggested three things about Christ that form the foundation of our assurance of salvation (his character, his work, and his promises).  If any of these things weren't true, we could never have confidence that we were his disciples.

Given that those things are true, how can I know that I am a partaker of those promises?  How can I know that his work is for me? 

I think we can start by looking for four things in our lives:

1. Faith in Christ today.  We shouldn't look only to a past profession, a prayer prayed, or an aisle walked.  Instead we should trust Christ today. (Colossians 1:23) 
2. The presence of God's Spirit.  Believers have the Spirit of God at work in their lives (Romans 8:9).  The Spirit leads us to believe the truth (I John 3:23-24), the Spirit bears fruit in our lives (Galatians 5:22-25), and testifies that we are God's children (Romans 8:14-16).
3. Obedience to the Word of God.  If we love him, we will keep his commandments (John 13:15).
4. A pattern of growth over time.  We should expect to see a (perhaps slow and erratic) but discernible pattern of spiritual growth (Philippians 1:9).  In David Powlison's illustration, the pattern of our life and growth may be like a yo-yo, but it‘s a yo-yo in the hands of someone walking up a flight of stairs.  There is a larger pattern of growth and maturity that God is graciously working in us—he is carrying us up the stairs. Even our low points now are higher than our high points used to be.

For what it's worth, I think it's best to pursue these questions in the context of a local church.  We don't always see the truth about ourselves (some are too easy on themselves, some are too hard).  We need other people to help us see more clearly.