In addition to the tasks outlined in First Month, here are some of the key tasks you should be accomplishing in the first 3 months (note that many of these tasks will require a copy of the death certificate).
If applicable, most executors start probate 2-3 months after the decedent's death. This process will get you an official document commonly known as your "Letters", which will make it easier for you to prove your authority when dealing with various other third parties such as banks. See Probate and Becoming Executor for more details.
If the decedent left behind dependent family members, and the estate is going through probate, you can petition the court to set aside a portion of the estate that can be made available to those family members to pay for their interim living expenses ... independent of any debts that the estate may owe. If such an allowance isn't necessary in this case, just mark the task N/A (Not Applicable) on the Tasks tab.
It will be easier for you to have the decedent's mail delivered directly to you. You can arrange this online via the USPS (for a very small fee), or you can mail a paper PS Form 3575 you pick up in person at a post office (you cannot print this form at home).
If you opt not to have the decedent's mail forwarded, you may at least want to minimize junk mail so you don't have to go through it (junk mail will normally get filtered out during the forwarding process). You can do this for free online at the DMAchoice Deceased Registry, and you can separately prevent unwanted credit card offers (it's easiest to use the 5-year "temporary" option).
Carefully go through all remaining mail. You will almost certainly uncover previously unknown debts over time, and it is your fiduciary duty to ensure that these are paid (or forgiven). You may also discover dividend checks, refunds, life insurance policies, and more, not to mention correspondence from friends who should be informed of the death.
If the decedent held any current life insurance policies, you may want notify the issuing companies, and ensure they payout in accordance with the terms of the policy. Often it is the beneficiaries that do all this, however, and the executor has no legal obligation in this regard.
A number of financial instruments, including IRAs and 401Ks, pass directly to the named beneficiary on the account. While the executor has no control over these assets if the beneficiary has been properly designated in the account, you should notify the account managers so that they can begin their proceedings.
While not mandatory, it's nice to clean up other official records so that the decedent's name doesn't later get entangled in various fraudulent activities:
Based upon the contents of a valid will, and/or local statutes, determine who the heirs are, and let them know. You will likely not be able to definitively tell them what, if anything, they will be inheriting until after you have determined overall estate solvency and sorted out various allocation questions, but it's nice to keep the heirs informed of the process (and required by law under certain circumstances).
You will need an equivalent of a social security number for the estate, in this case the inappropriately named Employer Identification Number (EIN). You can apply online for an estate EIN via the IRS, or you can obtain a copy of IRS Form SS-4 and mail it in.
While not strictly required, it's generally considered best practice to file Form 56 with the IRS, notifying the US government that you are responsible for the estate, and that all tax correspondence should go to you (reducing the risk of important mailings getting lost). When you have completed your executor duties, you will then file a corresponding Form 56, terminating your responsibilities, and this second filing will give you certain long-term legal protections.
You do not have authority to write checks from the decedent's account. Even if you had power of attorney, that generally disappears upon the decedent's death.
What you need to do is to open an estate account, with you named as the executor. While it would be convenient to do this immediately, you will almost certainly need to wait until you can provide a copy of the death certificate and an EIN, leaving you in an awkward state of having to pay for any interim expenses out of your own pocket, to be reimbursed once you can get access to the estate assets. Track deposits and withdrawals from this account via the Cashflow tab.
Probate publication is intended, in part, to ensure that any creditors get fair notice that they need to come to you to get their debts paid. If they do not contact you with a certain period of time after this publication, which varies by state, then they lose their ability to make any estate claims. Typically this response deadline ranges between 3-9 months, by state, and gives you protection against unknown debts that might otherwise surface long after you have distributed the entire estate proceeds. See Finding Debts and Task: Publish Notice of Death (sample Georgia estate).
If there are other acquaintances that haven't already been told about the death, it's nice to let them know (often in response to correspondence you will receive in the decedent's mail). This process can also be an interesting opportunity to learn more about your loved one's life.
You should have a pretty good sense by this point as to whether the estate owes more than it is worth, or not. If the estate clearly owes significantly more than it is worth, you may want to wash your hands of the whole thing, declare the estate bankrupt, and turn it over to the courts for disposition.
Some assets may be explicitly called out in the will for specific disposition. You may need to sell some assets to raise cash to pay off debts. Some heirs may want their share of the estate to include particular assets. You need to develop an plan that satisfies your legal obligations and preferably, maximizes heir happiness. See Managing Assets.
See also Calendar Year for tax-related tasks that may have to be accomplished within the first 3 months, depending on date of death.
Note that once you enter the decedent's date of death in the Decedent tab, and begin to fill out more information about the estate, EstateExec will calculate the relevant due dates for all of the listed tasks (and others), and display them in the Tasks tab.