Sorry to hear that!
I was executor for my mothers estate, so I understand where you are coming from.
The best solution in some respects is find a lawyer that is familiar with probate cases and let him handle lots of the details.
The desirability of that solution depends on how complex her estate is, and if she had a will.
You will want to make a list of all the businesses and institutions that she did business with.
Going through old mail for bills, and thumbing through credit card bills and check book will point you at a lot of things that you may not even know about like storage units, safe deposit boxes etc.
Some of the technicalities will depend on local law and business policies of banks and such.
Call her bank and sit down with an officer for an hour or so and they can help you with printouts of her checking/deposit transactions and list of her accounts and if she had a safety deposit box at her main bank.
Some people have legacy services at banks they no longer keep active accounts at so sometimes you will hear of people finding out a safety deposit box that has been in use for 20 -30 years at a distant bank exists,
It can also help to play 20 questions with her very close friends and relatives as sometimes things like special insurance policies, or property might crop up. It all depends on how she was inclined to take care of her personal affairs.
You will also want to check on the local legal notification laws regarding "legal announcements" of the closing of her estate.
In most states they have a requirement that a formal announcement appear in a paper of record, this sets a dead line for old creditors to present bills chargeable to the estate.
I took the relatively easy way and after talking to some friends found a small office attorney that specialized in estate work and he took care of 99% of the details simply calling me in to sign things from time to time. He wrapped up the legal side with out complications so I could focus on all the other issues like sorting through her things and giving stuff that had special meaning to the right people etc.
Don't let all the details over whelm you it is complex and time consuming but it will all get taken care of in good time!
Larry