The main reason FarmVille is so addictive is that at each level player requires different fixes.
This also makes the game a bit more interesting.
To achieve this you will require a balance of crops, trees and animals at each level.
You will have to study a lot to find answer to a ultimate question Mixed harvest or just one crop at a time? I will help you to clear your myths and find a answer to this question.
When you are at the entry levels of FarmVille quick harvester techniques described here will be helpful.
In the beginning just alternate between two crops instead of mixing crops that give XP with crops that give coins.
Keeping the plow, sow and harvest cycle at a pace will help you earn more coins and XP points.
For example one day you grow crops that give coins and next day grow crops that give good XP.
By this method you can keep a balance between all the aspects of the FarmVille.
If your farm is in a good shape, your growth will be more instrumental.
You can also add all kinds of farm upgrades and add the maximum allowed extra fields to get much more quicker harvest.
See the following illustrative example to know about a good FarmVille harvester to get more XP method:- Say you have 100 fields, and you harvest cheap quick harvesting crops ( the crops which harvest in one day) you can accumulate 300 points per day because you get 1 point per field and and another 2 for a harvesting field.
Next day grow a crop that returns in coins, keep it alternating for a week.
Remember if you visit your farms occasionally grow only slow growing crops because crops rot if you miss the harvesting window.