What is the proper procedure to charge a lead acid battery?
The bulk of the battery charge would be a constant current (CC) mode to the battery, this only gives you about 70-80% of the battery capacity.

If you want full battery capacity utilization you would then switch to a constant voltage (CV) mode.  If you wish to maintain the battery in a charged state you would then switch over to a lower CV float charge mode.  

The primary difference between the topping charge and float charge is the latter has a lower voltage, otherwise overcharge will permanently (if done long enough) reduce the battery capacity.

Lead acid battery charging voltage values are temperature sensitive, which can complicate things.

If you have a severely discharged battery, you will need to trickle charge it until it reaches about 75% of the normal battery voltage.  In most cases such a battery will have permanently reduced capacity.

Reviewing some integrated battery charge controllers such as Texas Instruments bq24450 or Consonance CN3717 is a good way to get introduced to the pitfalls as well.  Tim's recommendation will also give you good info.