Ella, several points (in my opinion )
1. Consistency (as mentioned) is the key.
2. Dehydrate yourself, no wee wees or drinkies for 2 hours hence
3. Test at 2pm if you can
4. Some women get a fade-in pattern (as mentioned). This is good! Means you have some early warning.
5. Most people have LH in their systems all the time, so that is why the line needs to be DARK
6. Some women NEVER get a dark line, maybe they are too dilute, maybe their bodies surge at a different time, or maybe that is just pot luck.
7. Temping might be more helpful if OPKs aren't working. At least it will tell you when you O, and that you O'd, but is not helpful to tell you when to expect O (and therefore BD like a mad thing). In this case, you will know more about your body in preparation for next cycle.

Oh, and I use internet cheapies which I find just perfect (cheap enough that you can use 2 a day for a while if you need )

Good luck sweetie!