Squirrels often follow wires or branches to a house, entering the home through an improperly covered vent in the attic or basement. The easiest way to keep them out is to tightly cover all possible points of entry on your house. Check under the eaves, around windows and any place vents are located to make sure all areas are covered.
If you find any spots where a squirrel might get in, cover it with hardware cloth, or wire mesh, fastened tightly on all sides. It's best to do this in the spring or summer, before the squirrels are looking for a place to hole up for the winter. If they can't get in they will go elsewhere to find a place to live. Be sure when you cover the openings that you don't trap any squirrels inside your house.
Since squirrels will dig up many kinds of flower bulbs, soak them in Thiram, a safe organic repellent, before planting. Make sure and bulbs you buy are labeled as a squirrel repellent; squirrels will naturally not be attracted to these bulbs. You can also plant daffodil bulbs, which squirrels don't like and tend to leave alone. To further deter them, place wire barriers over bulb beds, or make plant cages of chicken wire to prevent the squirrels from being able to reach the bulbs. If your yard is not attractive to them and there is not food supply, the squirrels will move to another location.
Use capsaicin (the component of peppers that makes them hot) to repel squirrels from your bird feeder. You can buy bird seed already coated with it, which is the best choice so you don't have to worry about getting the seed wet and possibly moldy by coating it yourself. It doesn't bother birds, but mammals such as squirrels don't like it. You can also use a capsaicin and water mixture to spray on young plants in the spring to protect them from being eaten by squirrels. This can wash off in rain, so plan on re-applying it on a regular basis until your plants are no longer attractive to squirrels.
Sometimes squirrels will chew on wooden deck furniture, railings, or other items which are commonly left outdoors. You can spray these with capsaicin, but as this can also affect people and pets---you don't want to get it in your eyes---a better choice is to use soap. Lightly rub any exposed surfaces with a bar of soap, and the squirrels will avoid the furniture, and often they will leave the area altogether.