I'll add a couple of things here.
Check the temp of the sample. Hydrometers are calibrated to be accurate at a certain temperature. There are conversion tables so that if you read your hydrometer with the sample above or below the calibrated temperature, you can convert the reading at that temperature to the correct calibrated reading. That said, the reading will always be more accurate at the correct temperature.
In general, take the reading from the bottom of the meniscus as shown in the link above. That said, not ALL hydrometers are calibrated this way. Some are calibrated to be read from the top of the meniscus. They will usually indicate one way or the other but if there is no indication read from the bottom.
All of the above advice is good but to add to that, consistency is key. If you're reading your hydrometer at 74º for SG, then read at 74º for FG. The accuracy of the reading at the homebrew level and for homebrewers is fairly irrelevant. You're looking for some indication of a starting gravity and a solid indication of end of fermentation. With those two readings you can calculate abv but it's not like you need to be within two decimal places for a lab or anything. Will you be able to tell the difference between a beer that finished at 1.010 vs 1.011? Not likely.
Just go with consistency in your readings.