Nineteen things that might help you scry, and one thing that definitely will

"Crystal-gazing shows how a substratum of fact may be so overlaid with mystic mummeries, incantations, fumigations, pentacles: and so overwhelmed in superstitious interpretations, introducing fairies and spirits, that the facts run the risk of being swept away in the litter and dust of nonsense." - Andrew Lang, Cock Lane and Common-Sense (1894)

Having read even a handful of books or articles on divination, I'm sure you'll immediately notice two things--authors tend to have strong opinions about what works, and their advice can be quite divergent and even contradictory.  For example, some people believe that it's difficult (or unlucky!) to read tarot cards for yourself, and other people maintain just the opposite point of view.  And since we're talking about the metaphysical here, there's no way to prove one right and the other wrong.  Here's a compilation of some of the "must do's" that I've seen or read over time:

• Leave your crystal, mirror or bowl out under the full moon to absorb its influence.
• Burn an incense that's suitable for your work. (Sandalwood, mace, and bay are some that are traditional for divination.)
• Invoke a god or spirit who can help you see what you desire.
• Inscribe your tool with prayers, words of power, sigils, or other formulas to enhance their efficacy.
• Gather scrying water from a sacred spring or other outdoor source.
• Place a light source behind you, so that it's indirectly reflected in the surface in front of you.
• Place a dark cloth or box around the speculum, so that no light is reflected in.
• Scry on a Monday.
• Scry during the full moon waxing moon, appropriate planetary hour, or astrologically favorable time.
• Scry at night, when your mind is closer to a hypnogogic state.
• Scry during the day, when you're less likely to fall asleep.
• Store your speculum wrapped your speculum in silk, to insulate it from outside influences.
• Rub mugwort on your speculum, smoke it, or drink it as a tea.  (Obviously, do your research before you ingest any herb.)
• Use chanting, drumming or singing to help you acheive trance.
• Make your own scrying mirror, so it will be uniquely imprinted with your essence and intention.
• Sleep with your tool under your pillow.
• Anoint your tool with a drop of your own blood to enhance the bond.
• Be a woman.  (Yes, it's a long-standing belief that women are more naturally seers, even though most of the famous ones throughout history have been men.)
• Recite a spell or rhyme before you sit down to scry.

And the one thing that will definitely help?

• Practice. (Duh.)

So far, I've avoided harping on the importance of regular, persistent practice in developing the ability to scry.  It's boring and obvious, and restating it over and over doesn't make it any easier to stick to.  But here it is, for the record:  The way to learn and grow in an occult discipline (or any discipline, really) is to do it--do it until you break through your resistances, do it until you find the methods that work for you, do it until your beginner's luck gives way to reliable proficiency.

As for the other ideas?  Some of them may work for you--the only way to know is to try them and see.  Just don't try them all at once.  Pick one or two at a time and keep a record of the results--that way you know what practices correlate with good results.  You can't really be scientific, but you can at least be systematic.