And there was a prophetess, Anna, the daughter of Phanuel, of the tribe of Asher; she was of a great age, having lived with her husband seven years from her virginity, and as a widow till she was eighty-four.  She did not depart from the temple, worshipping with fasting and prayer night and day. Luke 2: 36-37
Fasting.  The very word seems to give off a negative connotation.  Probably the first thing people think of when fasting is mentioned is “no meat.”  Or “deprivation.”  Or “ugh.”  
Fasting is a spiritual discipline.  In the Orthodox world, there is a word called “passions.”  A “passion” is something we love to do.  When we think of passions, we might think of things like “I have a passion for cooking” or “I have a passion for traveling,” or “I have a passion for singing in the choir.”  These are good things.  These are not the passions we are talking about.  
Each human being has a passion for lust, power, greed, ego, anger, etc.  These are bad things.  While we may not act on each passion each day, we will all struggle with each of these passions at some point in life.  The most basic of all the passions is hunger.  We all love to eat.  While I may not have an angry thought each day, or might be able to go days without a lustful thought, I can’t go more than a few hours without a hungry thought.  So, one of the reasons we fast is to tame our “passion” for hunger, and in training our bodies to go without certain kinds of food, we can train our minds to go without acting on certain actions, the “passions.”  
Why do we abstain from certain foods?  In Orthodox Tradition, when we fast, we abstain from any food product that contains blood—meat, fish, daily products, wine and oil.  Dairy products have trace amounts of blood in them.  Wine and oil used to be stored in the skins of animals and this is why we fast from them.  You can’t have wine but you can have grapes, you can’t have olive oil but you can have olives, because of how these products were stored.  Ideally in Great Lent, we fast from all blood products and the only blood that enters our bodies is the Blood of Jesus Christ, through the sacrament of Holy Communion.  This is the principle reason why we celebrate the Pre-Sanctified Liturgy that we mentioned previously, to fortify us in our fast by receiving the Body and Blood of Christ.  
Why forty days?  Because Christ fasted for forty days in the desert before His ministry.  And because Moses fasted for forty days before going up Mount Sinai to receive the Ten Commandments.  Why the rest of the year on Wednesdays and Fridays?  Because Christ was betrayed on Wednesday and Crucified on Friday.  
There is a time element to fasting that is often forgotten.  Centuries ago, when society was more of a hunting and gathering society, people would spend the majority of the day hunting for their meal, dragging it home, and cooking it.  During fasting periods, they would pick fruits and vegetables that they were growing in their gardens.  In the time they were saving, they were worshipping more and doing more charity work.  We’ve lost this time element during Lent.  We order a lobster instead of a steak and it’s still the same effort.  To keep the fast right, you should add a time element to the fasting—ADD something, like more worship, more Bible reading, volunteer one Saturday at a soup kitchen, etc.  
What if you can’t keep a strict fast?  Then don’t!  Fast in a way that is challenging to you.  If you’ve never fasted before, try something small that will be a challenge, like fasting Wednesdays and Fridays from meat.  If that is not a challenge, then try to fast from meat the first week of Lent and Holy Week in addition to Wednesdays and Fridays.  If that is not a challenge, then fast for the whole Lent from meat, then jump to not eating fish, and gradually increase the intensity of your fasting each year.  
The other comment I have on fasting, which I hope will not scandalize people, is that for many people, fasting doesn’t fix what trips them up spiritually.  There are some people who are addicted to pornography, x-rated movies, alcohol, weed, drugs, profanity, smoking, etc.  Fasting from these things during Lent (and purging them from your life after Lent) is going to do you a lot more good than fasting from meat.   
Fasting has to be combined with prayer, otherwise, it is just dieting.  So as you make a plan for Lent, you need to combine some kind of fasting with prayer, scripture reading and worship.