The main thing to remember with fasting, whether you skip only one meal or whether you fast all day, is that the point of fasting is to bring you closer to God. The time that you would have spent in preparing a meal and eating it ought to spent in prayer and meditation on God's Word.
I would not recommend fasting for more than 24 hours until you've tried shorter periods of time.
The best advice on fasting was given by Jesus Himself in Matthew 6:17-18...
"Moreover when you fast, be not as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Truly I say to you, They have their reward. But you, when you fast, anoint your head, and wash your face; that you appear not unto men to fast, but to your Father which is in secret: and your Father which seeth in secret, will reward you openly."
