what I should set for First_Lots_Size?

Important: (while changing the parameter First_Lots_Size from 0 to anything else please take care the following)
First_Lots_Size should be in the multiple of 2 X [minimum allowed lots size by your broker]
say,

• if your broker allows 0.01 lots then First_Lots_Size should be like 0.02, 0.04, 0.08, 1.14 etc.  [it shouldn't be like 0.03 OR 0.07 OR 1.11 etc......]
  
• but if your broker allows 0.10 lots then First_Lots_Size should be like 0.20, 0.40, 0.80, 1.20, 1.80 etc.  [it shouldn't be like 0.10 OR 0.70 OR 1.30 etc......]

What is the best appropriate value for First_Lots_Size?

calculate this: [amount required to open minimum allowed lots size in your account on 100:1 leverage] X 100
say, you need $10 to open 0.01 lots on your MT4 on 100:1 leverage, then the result would be, $10 X 100 = $1000
So now if you have approx $1000 in your account then you may set First_Lots_Size=0.02   [as 0.02 is the lowest possible value]
and on every increment of $1000 in your account balance you may increase the First_Lots_Size to 0.02
for eg. if your account grows to $4000 then you may set First_Lots_Size=0.08
{but try to set it small for very safe side}