It is a overwhelming task to begin organizing a lifetime of photos, letters, and other memorabilia. It isn't a project to take lightly, and sometimes it is hard to get started because you aren't sure where to start, how to organize or what you want the finished project to look like.
I've been working on my Grandma's history for over 15 years now, having started and stopped many times over the years, and technology has grown exponentially over the years, so I can understand the overwhelming feeling, but I can also personally testify to the excitement of finding a new picture that I don't ever remember seeing, or even just finding a picture that all of the sudden is a treasure, because I now understand it's importance.
This undertaking is so worthwhile that I'm going to offer a few tips for getting started.
Beginning with a simple timeline is a great place to begin to understand how everything else that you discover all ties together. I suggest a spreadsheet format, with the years listed down the left-hand side, and several columns with different headings. There are several things that you can include on a timeline, and you might want a combined timeline for a couple, with a column, or several columns for each of them.
Important/Special Dates - birth, baptism, graduations, wedding, birth of children, deaths, etc
Homes - what places did you live (this really helps with organizing pictures)
What is the final format of your project going to look like, there are many many options today, and will probably be more in the future. You can do a traditional scrapbook in either a 12 x 12, 8 x 8, 8.5 x 11, or 11 x 8.5 format. All of these sizes can be done digitally as well. You can also plan on creating a DVD with either a slide show, or an interactive DVD where you can click on links to learn more, hear music, watch video snippets, etc. Really, the sky's the limit as to what you can do, limited only by time, money, and expertise.
I choose years ago to design my pages in a 11 x 8.5 format because it fit nicely into a page protector in an inexpensive binder, the binders fit nicely on my book shelves, I could print them easily on any printer, and computer screens are in a landscape format so they are easy to design and view on a computer screen. I continue to design this way for many of the same reasons, but also because I want uniformity with the 1000 plus pages I have already designed.
However, there are now many places where you can get scrapbooks printed in a wide variety of sizes either as a bound book, or as single pages that you can slip into traditional scrapbook pages protectors and integrated with your paper scrapping pages.
The important thing is to make a decision as to what size you want to design in and for what reason. This does not limit you from occasionally making a different size ( for instance you may want to make a small 8 x 8 album of special family reunion) these pages could be re-sized for a larger album, 2 of them could be put on 1 pages, 4 on a page, etc with a new background layer to tie them together.