Unfortunately, I can't find the post I wanted to quote...had to do with "obese" people having bad veins...just personal experience, people don't look hard enough for them. I discovered this after my wife (who I had considered a hard stick because she was obese) had surgery, and lost 150 lbs, she now has "ropes" for veins. Now, obviously, they weren't small/not there and then suddenly there...and I've found (now I work in and ED FT) if I take a few extra minutes to look hard, I can usually find something sizable.
Some techniques I use: a double tourniquet...one a little more proximal to the first tourniquet (an IV tourniquet also works well for stubborn venous bleeds, place one as you would for an IV start just distal to the injury...works great!). This can help pop up veins. The biggest thing though, if time allows, is to LOOK. Look everywhere. In AZ, we can do ANY peripheral IV (an EJ is a peripheral IV) and 2 types of central lines (subclavian and IJ). I've found shoulders are a great source for veins, and I've even started (it was only a 22ga) in a very superficial vein on a quad's abd. The biggest thing is just spend an extra minute (if time/illness/injury allows) and you'll be surprised what you might find. Also, get out of the "box" with sites. If you can...feet are great (although shouldn't be used on some patients, but again, if it's all you got...and you absolutely need one). Sometimes, when I have a patient who needs an EJ, I will bend the catheter slightly (about 10-15 degrees from flat) to help with insertion...we use the INSYTE AUTOGUARD, which has a long, ungainly portion where the needle retracts by spring action. I have never needed to try this with other brands, but I don't see why it wouldn't work.
Also, if you think you are in, good flash, etc etc, but having trouble threading, you can try to float it in or you can "twist" the catheter off the needle, much like "screwing" it into the vein. Just be gentle.