Sunlight and Shadows
Long time gardeners pay attention to the strangest things. For example, they usually know when the last local frost is expected. They keep track of strange things like when the first frost of the fall is most likely to happen too. They probably know when they are standing in their garden which direction is east and west, north and south. There are very good reasons for them knowing all these things, this knowledge helps them grow a better garden.
Plants need sun to grow well, 6 hours at least and morning sun is usually preferred. So you need to pay attention to how much sun the various places in your yard get. Also morning sun means you need to know which way is east, where the sun rises. If you garden in the city as I do, it's also important to notice what blocks the sunlight. It may be blocked by trees, hedges, walls, fences or buildings. Also notice when these various things are shadowing your prospective planting area. Does that building block the sun in the morning, in the afternoon or the whole day? Don't worry you can almost always find a plant that will do well in a spot in your yard, however if you put a sun-lover in the deep shade it's not going to do very well.
Plants also need the proper temperature to grow well. Those walls, fences, hedges and buildings usually keep planting areas warmer or cooler than they would be out in the open. Go out and look at your yard. Notice the patterns of sun and shade throughout the day. Walk around your yard. Are there dips and valleys in your yard that will hold cooler air and might be frost pockets? Do you have a south facing slope that is good for heat loving or sun loving plants? Do you have too much sun and heat? Find a cool, shady north facing spot and you may be able to grow those cool growing, shade lovers. By knowing your yards micro-climates you can provide the proper growing conditions for your plants so they grow better with less effort on your part.