If you're depressed, what's the best testament to start with in the bible?

The bible has no treatment for depression. You get into therapy and handle it the way you are supposed to.

It is not reliable to let people tell you what the bible says. Many people will make up stuff because they don't know what it says, and many will make up stuff because they wish it would not say what it says. You just have to read it for yourself. Read a chapter of Proverbs every day. Proverbs has 31 chapters so you can keep your place by just looking at a calendar. There is no religion or nothing in Proverbs and you don't have to believe anything. Just read to find wisdom. When you are comfortable with that, then read the bible from Romans to 2 Thessalonians over and over until you start to remember what it says. That is the part that applies to Christians. Here is a book to help you to understand the bible. It's a free download and you can get a hard copy at any bible book store.
www.philologos.org/__eb-htetb/ "How To Enjoy The Bible"

It's very important to get help for clinical depression,for even Jesus said at Luke 5:31, "Those who are healthy do not need a physician, but those who are ill do." Remember God allow these doctors to be in their relevant positions so they could help people who needs medical help. On the other hand with medical help and help from God it is possible to beat or control your depression. So first step is to talk to your doctor . With your doctor help, and help from God's word you could beat your depression or at least have it under control. Let's look at a few scriptures that will be strengthening and encourageing for you :
Psalm 34:18---- 'Jehovah is close to the brokenhearted; He saves those who are
crushed in spirit.' Yes your Heavenly Father knows what you are
going through and is ready to help you, just talk to him, he is
listening.
Psalms 55:22---'Throw your burden on Jehovah, And he will sustain you. Never will
he allow the righteous one to fall.' God is willing to help you, all you
have to do is give him your problems, in your case allow his help
with your depression and he guarantee your medical help and his
help you will get some relief.
Psalm 65:02---- 'O hearer of prayer,to you people of all sorts will come.' Jehovah is
the hearer of prayer, keep praying to him and he will make a way
out for you or help you to endure your illness.
Psalm 103:14----'For he well knows how we are formed, Remembering that we are
dust.' Yes our Heavenly Father knows everything about us, that's
why he knows when we are hurting and comes to our rescue
when we keep calling on him.
Psalm 139:1,2,23 'O Jehovah, you have searched through me. You know when I sit
down and when I rise up. You discern my thoughts from afar.
Search through me, O God, and know my heart. Examine me,
and know my anxious thoughts." Only Jehovah have the ability
to read your thoughts and heart, so keep meditating on him on a
regular basis and he will be happy to converse with you.
Isaiah 41:10,13. I love all of God's words in the bible but this scripture is my
favorite., 'Do not be afraid, for I am with you. Do not be anxious,
for I am your God. I will fortify you, yes, I will help you, I will really
hold on to you with my right hand of righteousness. For I,
Jehovah your God, am grasping your right hand, The One
saying to you, Do not be afraid. I will help you. 'Jehovah is
emphasizing how much he wants you to lean on him. First he
said Do Not Be Afraid, then he said Do Not Be Anxious, I Will
Fortify You, I Will Help You. If that does not assure you,he says,
I Will Really Hold on to You With My Right Hand. Am Grasping
Your Right Hand. How reassuring Jehovah is that he knows we
could become a little anxious. Jehovah not only promises us
his help but he has the ability to do it.Trust him he has you.
Isaiah 55:6. 'Search for Jehovah while he may be found. Call to him while
he is near' You have an open line 24/07 to call on Jehovah,
use it and reach out to him, he will soften your pains.
Isaiah 57:15. For this is what the High and Lofty One says, Who lives forever
and whose name is holy. 'I reside in the high and holy place,
but also with those crushed and lowly in spirit. To revive the
spirit of the lowly. And to revive the heart of those being
crushed.'Jehovah is reminding us that even though he is the
Most High, never doubt how dearly he cares for you. For he
cares for you and holds you as precious in his eyes. He has a
very soft spot for those who are hurting. Talk to him and let him
know your desires.
James 4:8. 'Draw close to God and he will draw close to you.' What a
great previledge it is for the Grand Creator to offer you this
special invitation to become his friend. All you have to do is
meet him half way and you will form the best friendship ever.
You could talk to him, and rely on him because he is very
dependable.Never will he deceive you or forsake you. He
will forever be faithful to you.
Hope all the above info help you to take seriously your visit to your doctor and to build a close,relationship with Jehovah, the only one who could help you through your illness. For more,answers on this same topic or any topic you have please visit JW.org.