Stay Spread out over a 4 fret position
Always play on the tips of your fingers - just behind the fret with both joints of every finger arched.
This position will allow you to finger a single pitch without coming into contact with adjacent strings. This is an important technique, especially when playing double stops (two notes ringing out at the same time). If you don't use this technique, you are likely to mute out notes that you want to sustain.
Playing on your finger tips will keep you from having to remember to keep both joints in every finger arched in a "natural" direction. It is difficult to play on the tips without arches naturally occurring in the three joints of all four fingers. Many students have developed the bad habit of allowing the smaller joints towards the finger tip to arch back and lock into an uncomfortable and awkward position. Often the third finger is the greatest offender of this.
Don't do it!

Allowing the fingers to arch back is hard on your joints and will slow you down. The only time it is appropriate to lay your finger flat on the strings is when you are playing double stops across strings in the same fret or muting more than one string at a time. Even though baring your fingers across two strings is considered acceptable technique in many circles, you should pay close attention to any discomfort resulting from its use. A more classical approach may be less irritating on your joints and tendons.
When you play just behind the fret you will have more control of your sound because the flesh of your finger tips may have equal (+/-) contact with the string as the fret wire. You will have greater control of sustain, muting and vibrato, as will as less string buzzing, particularly when playing quick and aggressive lines.
If you have plans to play fretless or acoustic bass at any point in your career, playing on the frets now will leave you well prepared for the monster reaches and placement accuracy that is required by these instruments