Below are the zones for the USA, these are only guidelines, as of course the climate changes from year to year and even many an experienced farmer has been caught out by unseasonable weather changes.
If you are planning to grow to sell at a farmers market then the sooner you can display red ripe tomatoes the better. You will be able to ask a higher price as well. Remember the consumer will have been eating tasteless ones all winter long. Although we hate to think that the customer might damage what we are selling by picking it up, suggest they pick it up and smell it. The aroma will sell them even if the tomatoes don't look perfect.
Prepare your bed early with a high concentration of organic matter. Give this time to settle in before putting your young plants in it. A little preparation now can save hours of headaches later.
Source your sticks, cages, or other supports. It is no good running around at the last minute looking for these when your crop is beginning to fall over due to the weight of fruit hanging on it.
Remember to begin pinching off any side shoots once they start appearing.To get a strong central stem and a maximum crop yield, this needs to be done regularly.
Check your plants daily for insects and any other potential problems. We have all been there, where we go outside and discover a caterpillar, has chewed through a good portion of the leaves. It is downright depressing when this happens after all the preparation and work which has gone in to your plants. By checking the leaves on the top and underneath you will be able to keep these at bay. If you see butterflies, it is time to be extra vigiliant as they will undoubtedly be depositing their eggs on your plants.