How Do You Place Decimal's When Diving One Decimal Into Another? For Example: .7/.04

There are a couple of ways to do it.
1. Scale both numbers by the same amount so that the denominator is an integer.
  .7/.04 = .70/.04 = (.70/.04)*(100/100) =70/4 = 17.5
If you do the division the way I learned it, the quotient is developed above the dividend, so the decimal points of each line up. The first digit of the quotient goes above the least significant digit of the portion of the dividend that is being divided. In this case, 4 goes into 7, so the 1 in the quotient has the same place value that the 7 does. (If we were dividing .7/.042, then we would be looking at 700/42, and the 1 in the quotient would have the same place value as the 0 in 70, which is in the 10s place, as before.)

2. Express both in scientific notation such that the numerator is larger than the denominator (but not more than 10 times the denominator). Then, the exponent of the quotient will be the numerator exponent minus the denominator exponent.
  .7/.04 = (7*10^-1)/(4*10^-2) = (7/4)*10^-1-(-2) = 1.75*10¹ = 17.5
If you were dividing .7/.081, you would probably do it as (70*10^-2)/(8.1*10^-2) rather than as (7*10^-1)/(.81*10^-1). Either way, you recognize the first digit of the quotient is 8, and the multiplier as 10⁰=1.

This latter method is especially useful when the calculating tool is a slide rule, which mine was for many years. The calculator has changed all that, but I still use this method when the scaling of the answer is not obvious to me.