
I'm 20 over par almost every time I play (well, maybe not quite that much, but it's not unusual for me to be close to that on occasion). I also play mini golf as a way of practicing my putting and use one of those stupid little putting things, but although I think they help, it's just not the same as putting on a real green.
I think there are a million putting tips, starting from the basics to fixing individual problems with putting that you consistently have, but one of the best places I've found for help is a website called Dr. Putt (dumb, I know, but he's got a lot of info there). He's trying to sell an ebook, but if you get past that, there is a good Q&A section where people ask for help with specific putting problems. Also has a newsletter, but I haven't tried that to see if it's any use.
Here's the URL. Let me know if it helps.
http://www.drputt.com/index.html