The bare bones of Genealogy data is a gedcom file. Almost all family trees including PAF, Personal Ancestral File, from the LDS church, Legacy and many other programs have the ability to save your data and export it as a Gedcom file. So one of the most important things you can do when starting your research is to first send out an email to all your family and ask them for a Gedcom file of the information that has already been put into a program such as PAF. If you have an Ancestry.com subscription or some other account generally they too will have the ability to export that data. You may have to explain this to your family and help them out.
The last thing you want to do is to start from square one inputting every single person into a new program. I say this as person with over 200 cousins, 12 brothers and sisters and around 70 nieces and nephews many of the cousins and nephews are now marrying and just going to a Sunday dinner at my Dad's place is now feeling more and more like a weekly family Reunion! My family Gedcom file has tens of thousands of names so starting from scratch would not be wise.
So to make is easier on yourself you really ought to find out who is the one with the most info and start from that point.
But - and this is a big but as My Grandma Shirley Higham always used to say - DONT trust the data. Yep - get the data but only trust it as far as you can throw your laptop.
My family has done a terrific job with our genealogy. However, not all of the data has two primary sources attached and in reality that is what you want - each Person event should have at least two primary sources. I think my genealogy is very far off from that which actually makes the task of going back and proving each entry very daunting. I have not yet even begun to go out and find those sources.
Sources - with the advent of the web and all it entails each source should be actually attached to each Event/Person/Date etc. There are many ways of doing this from just typing out the source information to actually linking or embedding those images to the record. By the way, PAF, Legacy and other programs while able to be listed as the source and that can be helpful - are not primary sources! Primary Sources can be many things but they are not someone else documentation that such and such event belong to a particular person.
From the BYU PAF Tutorial - Of special interest are “primary sources.” For example, church records, land records (such as deeds), military records, probate records (such as wills), and vital records, and so forth, are primary sources. See more about Primary Sources Here.
The point here is that the Gedcom file is still the one thing in genealogy that remains solid. You should back up your Gedcom file often. I should note that the sources do not get included with the Gedcom file. In other word if you attach a census image, a baptism certificate etc. to a particular name you should type out the full source information as well as attach the file. The typed source will show up in your Gedcom file but not the photo etc.
Wikipedia has a great history and further explanation of Gedcom files.
Randy Seaver has also recently discussed some modern day problems with how Gedcoms are exported and there resulting data in a few different online trees.