There is a significant contingent of preachers who teach that if you are saved, the Holy Spirit's indwelling will necessarily produce changed desires, which will lead to a change in works. Therefore, your assurance of Salvation should be based on whether or not you see this happening in your life.
I would like to point out a few major problems with this teaching. Number one, the fruits of the Spirit (Galatians 5:22) will only manifest themselves if the believer cooperates with the Holy Spirit by walking in the New Man, hence the commandment given:
Galatians 5:16
16 This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
If this were automatic, and didn't require work on behalf of the believer, this commandment would be unnecessary.
If the Holy Spirit ever usurped your will to make you do some amount of good works, He'd do so all the time, and you would be 100% perfect. He would not play a game where He sometimes, for some reason, allows you to sin, and then makes you do some unspecified amount of works to prove you are saved.
If a believer couldn't choose to disobey the Holy Spirit's will for them, the following verses would make no sense either:
Ephesians 4:30
30 And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption.
1 Thessalonians 5:19
19 Quench not the Spirit.
Since it does take effort on behalf of the believer to walk in the New Man in accordance with the will of the Holy Spirit, it's a faulty basis for assurance. You are basing your assurance on your own imperfect efforts to fight against the flesh and walk in the New Man, which even Paul himself failed at frequently and habitually - Romans 7:14-25.
Therefore the idea that any "true believer" will have some undefined level of obedience due to the indwelling of the Holy Spirit is false, and implies a rejection of free will, which makes no sense unless the Holy Spirit is doing a lousy job, or playing a game with our mental health by making us behave only partially, for some unknown reason.
This is nothing more than a pseudo-humble way to teach works Salvation. If all of the person's good works are attributed to the Spirit, they can deny that they are teaching works Salvation while doing the very same. In reality, if the Holy Spirit is the only factor in why you obey, then all of the Bible's commands against sin become utter nonsense. The limiting factor is you, because you have to put in work after Salvation to serve God, hence why you'll be rewarded for doing so (1 Corinthians 3:13-15).
Secondly, if my assurance of Salvation is based on what I see in my own life, I can never have full assurance. This is because I can't know at what point I can be certain that my desires have changed enough to prove my faith was genuine.
Such a thing cannot be quantified - which is why proponents of this teaching never give a specific amount of works/desires that need to be performed. They just float out a hazy, undefined behavior or desire-based criteria for you to stake your assurance of your eternal fate on.
If I look at my life and desires, I will always find imperfections, many of them. And so how can I be sure that I've had a sufficient change? How do I know that my change is the work of the Spirit, and not my own carnal mind fulfilling the desire for something religious that is innate in every human being?
This is why this teaching is so dangerous. It sets people up for spiritual disaster by teaching them to put their assurance of where they will spend eternity in something as abstract and fickle as your desires, which are prone to corruption by the brain of flesh that processes them.
Or, if works and obedience are emphasized, I again point out that this will depend on a believer's choice to walk in the Spirit. Since a believer will never be perfect, there is always room to question whether you have enough works, and if the works are a result of walking in the Spirit or just an unregenerate man being religious.
This is usually "rectified" by some statement to the effect of "Well, you won't be perfect, but you will be able to see a change from before and after you were saved".
This presents a myriad of problems:
Therefore, comparing yourself to yourself is not a valid means of assurance, and comparing yourself to the perfect standard given by God (Matthew 5:48) will necessarily result in a lack of assurance for any honest person.
Since this false doctrine compels someone to look to their lives for assurance of Salvation, I want to point out the obvious - any unsaved person can clean up their lives, and start living in a better way.
There are millions of people who choose to stop various sins every day because of conviction of their God-given conscience (Romans 2:14-15), or otherwise realizing that sin has built-in consequences.
There are people that become very wicked, wind up going to prison, then get out and reform their lives. The amount of people who have gotten over alcohol or drug addiction is innumerable. Secular people give lots of money to charity, and unsaved nurses volunteer to good humanitarian causes overseas.
Many unsaved, works-trusting Christians decide to read the Bible more, or pray more, or go to church more often, or even become preachers for their false religions, feeling "led by God", they assure you.
Therefore, faith in Jesus Christ is not required to reform your life to be less sinful, or want do something good, or feel some spiritual desire, and so basing assurance that you have "real" faith in Christ in such a thing means nothing, and is foolish.
So, if not our works and desires, what are we to use to gain assurance of Salvation? Well, obviously a basis that is much more solid: the promises of Jesus Christ in the Word of God.
Here's one, for instance:
John 6:47
47 Verily, verily, I say unto you, He that believeth on me hath everlasting life.
If I lack assurance, I can look at that verse and ask myself:
"Have I ever trusted Jesus Christ to save me?"
Yes. Therefore either I have eternal life, or the Bible is deceptive beyond comprehension. I can repeat this with any number of verses (John 3:18, 3:36, 5:24, Ephesians 2:8-9, Romans 4:5, Acts 13:39, etc.).
The evidence that my life bears is irrelevant because that had nothing to do with my Salvation in the first place. My Salvation is based on the finished work of my Savior Jesus Christ, and that alone. I am not so foolish as to put my assurance in my own imperfect attempts to put off the Old Man and walk in the New Man, for reasons I've already explained.
I want you to walk in the New Man. I wrote an article dealing with the topic in-depth. However it is a terrible mistake to use that as a basis for your assurance. If you make that mistake, you will never have peace, nor assurance.