I would say do whatever it is you do...I just stick to my normal routine for that day. Basal testing on a week day can be different than on the weekend for some peaple.
smoking may raise your blood glucose level. I used to smoke and found that it did a bit (15-20 mg/dl).
If you only smoke occasionally, I would not do so during a basal test, especially since "occasionally" doesn't seem like it is your normal day to day routine. And, please, try to quit. I understand how hard it is, but it is not worth the complications, other health problems, and cost. I used Chantix and that really worked for me. It is your life, but at least think about quitting.
I walked into my first appointment at Joslin in Boston, told them I smoked and they actually said, "let your last cigarette be your LAST. You will lose your legs." It was a scare tactic, but it worked. Six years later, and after several failed attempts, I was finally able to quit!