The following quote is from Spiritual Depression by Dr. Martyn Lloyd Jones. I hope you find it as helpful as I have.
We look to Christ and to Christ alone, and not to ourselves in any respect whatsoever.
To make it quite practical let me say that there is a very simple way of testing yourself to know whether you believe that. We betray ourselves by what we say. The Lord Himself said we should be justified by our words, and how true it is. I have often had to deal with this point with people, and I have explained the way of justification by faith and told them how it is all in Christ and that God puts His righteousness upon us. I explained it all to them, and then I have said: ‘Well, now are you quite happy about it, do you believe that?’ And they say, ‘Yes’. Then I say: ‘Well, then, you are now ready to say that you are a Christian’. And they hesitate. And I know they have not understood. Then I say: ‘What is the matter, why are you hesitating?’ And they say: ‘I do not feel that I am good enough’. They are still thinking in terms of themselves; their idea still is that they have to make themselves good enough to be a Christian, good enough to be accepted with Christ. They have to do it! ‘I am not good enough.’ It sounds very modest, but it is the lie of the devil, it is a denial of the faith. You think that you are being humble. But you will never be good enough; nobody has ever been good enough. The essence of the Christian salvation is to say that He is good enough and that I am in Him!
As long as you go on thinking about yourself and saying: ‘Ah, yes, I would like to, but I am not good enough; I am a sinner, a great sinner,’ you are denying God and you will never be happy. You will continue to be cast down and disquieted in your soul. You will think you are better at times and then again you will find that you are not as good as you thought you were. You read the lives of the saints and you realize that you are nowhere. So you keep on asking: ‘What can I do? I still feel that I am not good enough’. Forget yourself, forget all about yourself. Of course you are not good enough, you never will be good enough. The Christian way of salvation tells you this, that it does not matter what you have been, it does not matter what you have done. How can I put this plainly? I try to say it from the pulpit every Sunday because I think it is the thing that is robbing most people of joy of the Lord. It does not matter if you have almost entered into the depths of hell, if you are guilty of murder as well as every other vile sin, it does not matter from the stand point of being justified with God. You are no more hopeless than most respectable self-righteous person in the world. Do you believe that?