Chunk syllables and memorize the syllables by spelling them aloud and in rhythm. For example, break the word "icicle" into three rhythmic chunks, ic-ic-le. Break the word "superfluous" into these chunks: super-flu-ous.
Write any words that don't follow phonics rules in the palm of your hand with your index finger. Trace the letter and feel it while saying the name of the letter. Then make a fist to get control of that hard to spell word.
Match the word to another word that has a similar spelling to learn more than one word at a time. For example, learn to spell "measure," "pleasure" and "treasure" at the same time. Memorize "hoist," "foist" and "moist" all at once.
Spell words in the air using large movements, or trace the letters on the floor with your foot while saying the name of the letter. Get your whole body involved in learning a hard to spell word.
Study for short sessions frequently. You'll be more apt to remember what you've studied if you look at the material often for short periods of time over a week or more rather than for a long time right before a test.