What You'll Need
First, print out some blank family group records. I use the one from Ancestry.com because it includes a cause of death field, but there are many free family group record templates available online. Byub.org and NewEnglandAncestors.org both provide free family group records, or you can search Google or even make your own custom form with a spreadsheet program if you can't find one you like.
Second, you are going to need your sources. Physical sources should always be kept together in an easily accessible location. The sources you find online should be downloaded if they are scanned images or PDFs, or recorded in a notebook or text file if not a downloadable resource.
Start Filling in What You Know
Go ahead and fill out a family group sheet with your parents as the husband and wife, and you and your siblings as the children. Only enter the information you have sources for, such as your birth certificate (which you should have by now, if not, order one from your local county court house), family bibles, marriage records or what you are absolutely certain of.
For example, I don't think it is imperative to get copies of your siblings' birth and marriage records if you have had enough experience with celebrating their birthdays and anniversaries to know the dates. However, it sure won't hurt if you can get them. Even an email from your siblings giving the dates and places of major events in their lives will suffice as documentation, just be sure to print it out or save it to your computer.
You will, if not right now, eventually, want a record of your parents' marriage. If you don't already have it, add it to your "to do" list. Same with death certificates, if either of your parents or any siblings are deceased.
Continue in this same manner with your grandparents' family units and so on.
Cite Your Sources
You can do this on the back of the family group record. Simply write down the documents or other sources where you obtained the information (your birth certificate, a family bible, a transcribed interview with a relative, etc.), and where the source is located (in your possession, on your computer, the county clerk, the genealogy library, etc.).
Also indicate what information was provided by each source, as some documents will provide data on more than one event. For example, a death certificate usually contains birth date, birth location, death date and location, parent names, cause of death, and burial information.
Keep Your Family Group Records Updated
Every time you discover new information about an individual in your pedigree, update your family group sheet. This is why I always recommend filling these out in pencil.
You may, as I have, discover that the birth date you found on a death certificate is in conflict with a birth record you recently found. The birth record would take precedence over the death record for the birth date because it was recorded closer to the time that the event happened.
Using Your Family Group Sheets
The best part about having a family group record for each ancestor in your line is that you will have quick access to the names of their children. This will aid you in searching for extended family, which can give you great clues in finding out more about your lineage.
For example, many times older relatives would go to live with one of their children if they were no longer healthy enough to take care of themselves. Knowing all of a grandparent's siblings' names and data may help you find where a great grandparent lived out the remaining years of their life, especially if that great grandparent had a tricky name that was often spelled differently from one census to the next (yes, I'm talking about you, Miss Bettie Camilee Markham ;)).
Keep your family group sheets together, and bring them where ever you do research, whether it is on the computer, a genealogy library, a relative's house, or any place your think you might find sources.
You will also be able to use your family group sheets when you begin entering your family tree information into a genealogy program, but we will get to this later.
Question: How important is it to get official documentation on your own living siblings, and why? Please share your opinions and views in the comments section.