It is well known that spiders spin the most fascinating and bizarre things while intoxicated. Marijuana, alcohol, and many other drugs will cause a spider to spin wild, patternless trash.
Convincing a spider to spin lace is far more difficult.
First, one must put the spider in the proper frame of mind. Your spider should be installed in the parlor. Frequent salons should be held; between salons, play audiobooks of Regency romances for your spider. If you treat your spider as a lady, she will act as one.
Secondly, one must prepare her food in an appropriate manner. Keep an aquarium full of flies; instead of water, give the flies tea. Earl Grey is preferred, but any proper black tea will do. (Green or red teas will produce markedly different results. Herbal teas are not recommended.)
Thirdly, while your spider is devouring her tea-filled fly, sip cognac (port will do in a pinch) and exhale gently across her web. This will make your spider pleasantly tipsy - not enough to get her drunk, just enough to make her feel quite agreeable.
Whisper your request to your spider. Politely. She will comply, spinning loop after loop of the most intricate lace. When she finishes, she will bow slightly; bow in return. With her permission, and after transferring her to a new web, sever the lace from the web and dip it immediately in the preserving agent of your choice. Treated properly, spider-lace is perfect for hats, samplers, and the edging of gloves and bodices.