pj makes a good point. It can be very involved. So to single out your weaknesses would be best.

Every one else makes good points too.

As ataraxis said. develop a strong middle.
Castle early if you can. (This brings the Rooks out and protects your queen.)
Don't be afraid to exchange pieces, But pieces generally have a point system, meaning which ones are most important. Queen - Rook -bishop etc.

Computer chess will not give you the feel of playing chess from an individual. It is too systematic.
When you play with a person they (assuming they are not a chess master) will make odd uncharacteristic mistakes. Ones you will not at all familiar with, if you play with a computer. IMO.