The Medium-Medium system has its variations, but in its simplest form is for someone who wants to spread out their play and wants a lot of plays everyday. Basically it is for spread sports (Basketball/Football), what it entails is picking a number in the medium values that you feel comfortable with, most pick 3.0 or 3.5. Then you just bet every single medium value games, totals and sides everyday at the multiplier you have established.
So for example if your multiplier is $10 then if you see a 3.5 value and a 4.3 value you would bet $35 on the 3.5 and $43 on the 4.3. Now you must be thinking 'what about the vig', 'shouldn't you bet $33 and $44', you could, but the multipler is just for simplicity's sake. You get a lot of plays with this betting system, so you should be prepared for a lot of betting. Some days you might have only 2 or 3 but on some days you might see 20 or more. You need a bankroll and patience.
There are some variations of this system, which is breaking down the medium values by specific other indicators. For example...
There are limitless variations, but the system is still based upon some Medium-Medium value level and up.