Make sure that your test tube is as vertical as you can get it, and put your sample+hydrometer into that. The meniscus is the "collar" or bent up liquid around the edges of the tube, and around the hydrometer on the surface. It is caused by surface tension in the liquid. Your illustration shown above is correct - don't measure where the liquid curves up to touch the instrument, instead try to see where the sample is flat and try to figure out where that level of liquid would bisect the instrument's graduation marks.
If your hydrometer is different and calibrated to the meniscus instead of how all others are calibrated, fill the tube with ~70F (or whatever temp is says it is calibrated to) distilled water and re-measure. If all is well, it should be exactly 1.000.
Grab a couple or 3 sanitized turkey baster's full, put them in your test tube (usually the tube the hydrometer comes in works great), put in the hydrometer, spin the instrument to fleck off bubbles, and do the stuff above. Drink up the sample when finished.