Pattern pieces: If your pattern pieces are half ones it's well worth doubling them to make full pattern pieces, that do not need to be placed on a fold. This is useful for many reasons; one is pattern placement when it comes to lining up lace motifs, another is getting the most economical layout on a small piece of possibly expensive lace.
Also if your pieces are to be cut on the bias... some knickers patterns are suitable for fine wovens like Liberty, and need to be cut on the bias and it's only about 1000 times easier with a full pattern piece than folding the fabric accurately for a "cut on the fold". Mark the bias line on all new pattern pieces too.
Usually I save paper by taping together scrap pieces or even newspaper to make the other half pieces; for frequently used patterns, or if the original is a fragile tissue paper pattern, the pieces can be traced as whole new ones on thin, sheer plastic which is more durable (above). For this I use plastic table-clothing, sold in 30m rolls from the party section of Spotlight.
Also, I jot on the actual pattern pieces the lengths of elastic needed, to save re-measuring for each new project.
When sewing the ends of the rings and sliders; cut, pin and sew the pairs together and at the same time. It's hand down the best way to guarantee the two sides will be identical, if such things as symmetry are important to you. Actually the same goes for anything there will be a "pair" of in the project.
Satin ribbon trim; I always "heat seal" the cut ends of ribbon bows so they don't fray during wear. Just hold the cut end of the ribbon close to a candle flame and carefully watch it as you sloooowly move it closer; it gets to a point where it starts to melt away in the heat. This happens pretty quickly so you need to keep a close eye on it and pull it away the very second you see it happening.
Hook and eye tape: I prefer to buy separate hook and eye tape if it's available but my closest store sells only "bra extenders". I've found these to be an adequate substitute if I can't find the proper arrangement; the pieces can just be picked apart quite easily. If the "hook" piece is too long the extra length can be cut away and the edge zig-zagged. It's not as neatly finished or as professional looking, but it's perfectly fine in a pinch.
Sewing edging elastic onto lightweight and super-stretchy fabrics ...
Super stretchy fabrics are obviously perfect for underthingies but also obviously come with their own little challenges... and one of them is the dreaded "lettuce leaf" edge happening.
yes, this is my own work *hangs head in shame*I've found it very helpful to sew a long basting or stay stitching 6mm (1/4") from all edges before attaching any elastic. I know, straight stitch on knits, *horrified gasp* it's a huge no-no and I could get blasted for this! but meh, it works out pretty good for me :)
I mean, everyone has their own, slightly unique way of attaching elastic, I'm of the school of thought that whatever works, works; and lots of different ways are going to work.
The lettuce leaf occurs when the elastic is overstretched while sewing it to the edge of the fabric, and it's pretty easy to do this when sewing with a particularly stretchy fabric. It's better for the elastic to be sewn to the edge of the fabric "flat" that is, for the elastic to be stretched to the minimal amount and for the fabric to be stretched not at all, while sewing them together. A stay stitching helps to prevent this, and after the elastic is attached and before the final zig-zag you can pull out those initial basting/stay-stitching threads, if you like; to keep things looking nice and neat and tidy.