Has prior possession charges
Any self help will go mitigate sentence but the range of sentence depends on the charge and the priors.
It can't hurt, but it won't make the charge to away. How much it helps depends on many factors. A good lawyer will help even more.
Criminal Defense Attorney
Will make the person more presentable in court as it shows an effort to try to "clean up." However, the charge will remain the same. This might help the prosecutor in offering a better plea and can help at the sentencing phase of the case. Have him/her seek out a criminal defense attorney.
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DUI / DWI Attorney
Will make the person more likable in court as it would show effort in trying to clean up their lives, but the charge will remain the same. In that case, you could get a better plea offer and a lesser sentencing if the Judge has discretion. Hire a good criminal defense attorney.
Do NOT rely on this answer as the information provided here is not legal advice nor is it a substitute for legal advice which requires a consultation with a lawyer. This response does not create an attorney-client relationship.