Most fresh tomatoes sold in supermarkets are firm, not yet ripe. This is because soft, ripe fruit is easily bruised, even under today's highly-controlled shipping conditions. Use the ripest fruit first, just as your do with bananas and avocados.
Cold temperatures destroy flavor and stop the ripening process.
To enjoy fresh tomatoes at their peak of flavor, use when fully ripe. Ripe tomatoes should be completely red or reddish-orange, depending on variety. They will have a sweet, subtle aroma and will give slightly to gentle palm pressure. To hasten ripening, place fresh tomatoes in a brown paper bag or in a fruit ripening bowl. This gas speeds up the ripening process when confined around the fruit in a closed bag or fruit ripening bowl.