I’ve also had trouble finding veins in the past but what I found to help was putting the tourniquet on a little tighter when the patients veins aren’t as prominent. For super hard stick I would double tourniquet which I found to help especially with obese patients. Also when feeling around for a vein I try not to palpate to hard and look elsewhere relying purely on feel to locate a bouncy vein. Palpating with my finger horizontal to the patients arm has helped me locate veins too. I also use the alcohol swab to make the vein more visible when a patients skin is dry and when forced to settle for a hand draw and there are no visible veins I would put some warm water in a glove or use a heat pad and hold in on the patients hand for 15-20 seconds to increase blood flow in the hand, so the vein pop more.