Trees have different needs from other types of plantings. Trees need canopy space, sun, air circulation, and clear distance from man made structure which might include buildings as well as sidewalks, patios and pavement.
Once you have selected the tree to be planted, find a reference source that gives details of the mature tree. Plant so the trunk of the tree is at least 10 ft from any structure. Even with a 10 foot distance to a structure, be aware that the tree canopy may hang over the structure. In areas that may be threatened by wild fires, the overhang, more than the trunk distance, may be more important. In these cases, it might be advisable to plant the tree so that at maturity, the drip line is more than 10 feet from a building. The dripline is the area directly located under the outer circumference of the tree branches such that if you were standing under a tree at the beginning of a rain, the area within the dripline would stay dry for a while. The page of this Urban Forestry information has numerous links that list tree details with size and spread.
Plant in an area that gets at least 6-8 hours of direct sunlight. While some other types of plants may grow in shade or filtered light, trees need direct sunlight.
Trees need good air circulation. Good air circulation minimized the susceptibility of the tree to leaf diseases. Try not to plant in an area completely surrounded by buildings.
Trees have most of their roots in the first 18 to 24 inches of soil. If the soil is very shallow, perhaps the level can be raised so the roots can grow. Tree roots can spread from 1-1/2 to 4 times the height of the tree. Consider that space when planting a tree. Special provision may need to be made when planting in small cut-outs in sidewalk areas, parkways, parking lots, and street dividers.
Trees need well drained soil. Do a drainage test on your anticipated site. Dig a hole 18 inches in diameter, 12 inches in depth. Fill the hole with water and let it drain. After it has drained, fill it again and time how long the hole takes to empty. 1/2 to 4 hours is good, 5-12 hours in moderate. If over 12 hours, there is a problem. If drainage time is greater than 12 hours and the site will still be used, a raised bed of appropriate size may be the only way the tree can be grown successfully.
Also consider the presence of utilities. Look overhead for potential conflict with power lines. Underground utilities like gas, water and power may come in the way of growth of mature tree roots. DigAlert, a no fee service for locating underground utilities in Southern California, at (800-227-2600) will help identify potential utility conflicts.
If at all possible, do not plant in turf areas. If the tree must be planted there, clear the turf for a radius of 2 feet around the trunk and maintain that cleared area.