Wow...finally a post that I know I can answer!!
I am a member of a club that gives away quilts for charity. ALL of our quilts are tied. How you tie depends on if you are doing it in a frame (which is easier) or on the floor/lap.
If not using a frame, make sure that it's pin or thread basted very well. A very safe rule of thumb is no matter the thickness of the batting, place a tie on each side of your fist. Make a fist and put it down on your quilt and measure with it. After you've done that for a while you will be able to gauge if your fist is too big or too small. Sometimes what I do is use the fist plus an inch or so on each side and go all the way across in a row that way. Then, the next row I put a tie in between the ones I already made but up in the second row. I repeat the alternating ties and then it'll resemble a checkerboard a little bit. It's a nice pattern to use. Sometimes, the quilt top will tell you where to tie. Sometimes you could use the print on a fabric or keep tying in the same pieces of blocks over and over again and make a pattern that way.
Back when I was working, I had an understanding employer that would let us do whatever word searches, crafts etc at our desks. (Telephone operator). I would make sure the quilt was pin basted everywhere that I wanted a tie. Then I took it to work and tied it on my lap. Since it was already pinned so well I didn't need to worry about pulling tight or anything like that and they always turned out nice.
Hope this helps..
Melissa