Hello,

With drainage, you need to think in terms of 3 things:

1. Get the water into the pipe,

2. Get the water through the pipe,

3. Get the water out of the pipe.

To get the water into the pipe, you need to identify where the water is coming from.  If you have a flat lawn and the water is coming from rain, as opposed to a hillside slope, then it is very difficult to drain because the water will not move very quickly through a clay soil into drain pipes even if they are installed. 

However, installing French drains will help some with the biggest benefit being that your lawn will dry out more quickly in the spring once the rains stop. 

French drains are simply a trench which is dug, ideally, perpendicular to the slope with a pipe in the bottom and the entire trench is then backfilled with USGA specification sand.  If there are multiple pipes then they are often attached to one main pipe on the side which carries the water away.  The sand can be purchased from either Fazio brothers or Walrath sand and you have to specify golf topdressing sand.  If you buy sand from a local quarry, the sand will likely not drain.  It is absolutely essential that you get the correct sand.  The correct sand gets the water into the pipe assuming the water is getting to the top of the French drain.  A surface slope greatly helps move water into French drains because the water will travel across the surface.  Therefore, re-grading your lawn with slopes can be a great help.

The other key points are that the pipe has to run down hill (1% slope) and it has to have some type of an exit point (i.e. the water has to go somewhere) This is getting the water out of the pipe - point 3 above.  You can rent a lazer surveying tool to ensure that the pipe is running down hill.  The slope can be created by changing the depth of the trench.  Buying stiff drainage pipe (it needs to be perforated - i.e. with holes) ensures that the pipe is not placed in the ground in a wavy fashion.  After trenching, put some sand in the bottom as a smooth, protective base from rocks and place the pipe in the trench with the holes on the bottom.  Use the surveying tool by placing the measuring stick on top of the pipe every 5' or so to ensure it is running down hill.  After filling in the trench with sand, plant grass in the sand (do not use sod).  Over time the grass can build up an organic layer.  If the layer gets too thick, the water will not move into the drains, in which case you would need to sod cut the turf and replant grass (Perennial ryegrass) into the sand.  Dethatching every year will help prevent an organic layer buildup.

In some situations, a sump (large hole) is created and a pump is installed to pump the water where it needs to go, possibly to the sewer drains or the stree

Drain pipes are normally installed 10 feet apart, but the closer the better.  If you have a slope for the water to move across, then French drains will be more effective.

The one caveat about French drains is that they will dry out more quickly in the summer because they do not hold water.  Often times this results in a stripped pattern where the grass is drought stressed and you can see where the drain lines are installed.

I hope this helps.  Good Luck.