I use perle cotton crochet thread now but used cheap acrylic yarn on the first few I tied. The acrylic is slippery, though and some claim it can untie itself.
I use a tapestry or soft sculpture doll needle--something with the biggest eye I can find and still be sharp. I sometimes have to iron the thread to fit it through the needle.
I make a design with the ties so mine vary from 2 to 6 inches apart. Center of block, corners, certain patches within the block, only in the sashing, whatever works for me. I have also tied part and quilted part. I use the double granny knot to tie my threads. I have tried to do the long thread, stitch, jump to the next spot, stitch, etc. but pulling those long lengths of thread through is tiring. Sometimes I can get hubby or my daughter to help and they clip with I stitch so the long thread gets snipped as I sew. That works really well.