As I said I use a method I refer to as the filter or papertowel method. The filter method is also known as Deno method (Norman Deno). There are many other names for it too, I am sure.
The first thing you will need is your seeds and how many you need for your garden per previous calculations. The one that will require more than 1 baggy is peas and perhaps corn if you are doing that much. I don't know that you will do all of your peas at one planting or a series (which is what I plan to do). If you do it all at once, the recommended number of peas is 150. To give your seeds the room and moisture needed for germination, I recommend breaking this into at least 4 bags or even 6. Also since peas are larger seeds, I would use a papertowel instead of or in conjunction with the filter, just to give it enough moisture. In my series of plantings with peas, I intend to start 20-22 of each of my varieties.
Then I get out my filter (and a papertowel for moisture mentioned above), fold them to fit in the baggie (by laying it on the bag) and dampen them with unsoftened water - the water where I live is HARD so we have a salt softener and I don't want that salt in my gardening projects. I won't go into folding it, because each person has a preference, so use your own, but the seeds will be "growing" in this, so make sure you can unfold easily.
Taking your seeds place them in the folded filter, and with the papertowel (if using one) place inside the baggie. Wipe off the outside of the baggie with a dry towel so that you can label it with name, date and number of seeds. As I said I use a dry erase marker - some people use a sharpie. I just am careful when handling the bags so I don't wipe them off.
I usually start the germination process two days before the date I indend to plant. So I will do my starts on saturdays and planting (either indoor or outdoor) on Monday. Some people let them go longer than that, but I don't like to let them go beyond that as they mold or grow into the filter/papertowel.
A great hint I just picked up was to store the baggies upright. This is a great tip because then your seeds all germinate in the same direction, with the root going down and not into the filter/papertowel.
This method works for me, but if it isn't to your taste, use what works for you.