Note: The easiest way to wreck your case is lying. We can argue the semantics, but this also includes withholding information.
You should never withhold information from your lawyer if there is any chance that information could affect your personal injury lawsuit. It is better for your lawyer to receive potentially damaging or embarrassing information from you than from the insurance company or opposing counsel. “Top 5” things you should tell your attorney:
- Your Criminal History
- Prior Accidents, Injuries and Illnesses
- Subsequent Accidents and Illnesses
- If you File for Bankruptcy
- If you File for Divorce
Tell Your Lawyer Your Entire Criminal History
At your initial meeting with your lawyer, you should disclose your entire criminal history. 
Most of this information doesn’t make a big deal on your case, but you don’t know unless it’s discussed. Your attorney generally will not run a background check on you, but you can bet the insurance company and the opposing counsel will. Your lawyer should not hear about your criminal record for the first time when opposing counsel asks you about it at your deposition (and the defense attorney will ask).
Convictions for misdemeanors involving dishonesty (such as fraud or theft) and all felonies can be used to impeach your credibility as a witness. If your lawyer knows in advance about these convictions, he or she can help prepare you to answer questions about them. If the convictions are sufficiently old (more than 10 years usually) your lawyer may be able to keep them out of your trial entirely. I advise that you disclose all arrests and let your lawyer determine whether they are relevant to your case. Most lawyers do not balk at a client with some criminal history. Of course, if you have recent convictions for insurance fraud, you may (and probably should) find that no lawyer wants to represent you.
Tell Your Lawyer About Prior Accidents, Injuries and Illnesses
Your lawyer needs to know what condition you were in before your accident to determine what injuries can be claimed in your lawsuit.
To get a complete picture of your pre-existing conditions, your lawyer needs to know about all prior accidents (car accidents, slip & falls, work injuries, etc.), regardless of the type of accident which caused your current injuries. In fact, you should tell your lawyer about any chronic medical conditions, even if they were not caused by an accident. You should also tell your lawyer about any prior mental health treatment, as this may affect any emotional distress claim you may have.
All of these prior accidents and illnesses will come out through your medical records or through opposing counsel’s background check, so there is no point in trying to hide them from your own lawyer.
Tell Your Lawyer About Subsequent Accidents and Injuries
As with prior accidents and injuries, you need to tell your lawyer if you suffer an injury after the one for which you are filing your lawsuit.
Some subsequent injuries may be relatable to your lawsuit, such as a fall that was caused due to the knee you injured suddenly giving out.
If you are involved in a minor accident after your lawsuit is filed, such as a fender bender, you still need to let your lawyer know about it. If you don’t disclose the fender bender in your lawsuit, it will eventually be discovered by opposing counsel and it may appear that you are trying to claim injuries from the subsequent accident in your current lawsuit (even if you suffered no injuries in the subsequent accident).
Tell Your Lawyer if You File for Bankruptcy
This is a big one. If you file for bankruptcy at any time after your accident but before your lawsuit is settled, your personal injury lawyer needs to know immediately.
Filing bankruptcy does not necessarily mean that you won’t recover anything from your lawsuit. There are certain bankruptcy exemptions ($50k in Oklahoma) that will likely apply to your lawsuit that may let you recover some, if not all, of your damages despite the bankruptcy. If the applicable exemptions make it appear that your bankruptcy estate will not receive any money from your lawsuit, the trustee may just give up on your lawsuit and not pursue anything from it.
Tell Your Lawyer if You File for Divorce
If you file for divorce while your lawsuit is pending, your personal injury lawyer needs to know. He or she may want to depose your soon-to-be-ex-spouse before hostilities erupt (or escalate).
Also, if your accident contributed to your divorce (e.g., from loss of your job or a change in your personality due to your injuries) your divorce may increase your emotional distress damages (as well as your spouse’s loss of consortium damages).
Some of your damages (such as prior wage loss) may be subject to division in the divorce. Your lawyer needs to know this before distributing any settlement money.
When in Doubt, Tell Your Lawyer Everything
If you have any doubts as to whether you should tell your personal injury lawyer something, always err on the side of disclosure. Your lawyer is not there to judge you, and he or she really only cares about how the information you provide may affect your lawsuit. All of your disclosures will be kept confidential due to the attorney-client relationship, and failure to disclose information will always be worse for you than over-sharing.