A banana should be complete yellow when ripe. A banana with a lot of brown spots tastes better than a yellow banana with a green top. Bananas are brown when overripe and green when not ripe.

Put bananas in a fruit bowl in the sun to ripen quickly.

For more information on bananas click here.

Cantaloupes & Honeydews

The ripeness of cantaloupes and honeydews can be determined in four ways:

1. The best thing you can do is smell. This doesn't apply for watermelons. Watermelons are described below. As for cantaloupe: don't look, don't touch, just smell. Ripe cantaloupe smells very sweet and nice. Sniffing out the most aromatic one is the smartest way to pick a cantaloupe or honeydew.
2. Thump test: hold your dominant hand as if ready to knock on a door. Deliver two or three good thumps to the round side of a melon. The sound should be deep and thick, indicating a dense, full fruit. A higher hollow sound can mean unripeness.
3. If a honeydew is beige-skinned with distinct green veins it's probably not ripe yet. If it has a pale yellow color with bright, lemon-colored areas you probably have found a good one.
Cantaloupes are unripe when the skin beneath the textured "web" is green. Cantaloupes are ripe when orange or gold.
4. Another mark of desirability is a patch that's slightly flat and bleached in color. Melons that develop on the vine flatten under their own weight, and lose color where they sit on hot soil. In general, stem ends should be moist, not moldy. A good melon is firm, but not rock hard. It yields very slightly to pressure but has no soft spots.  
5. Ripe cantaloupes rattle only occasionally, so it's an unreliable indicator. 

To determine ripeness of cantaloupes and honeydews in order to pick them from the plant, the following indices of maturity are known:
Grasp it firmly, give a tug and a twist. If it falls easily off the vine into your hand, it's ripe. 

For more information on cantaloupe, honeydew and a lot of other melons click here.

Oranges

Oranges color orange under the influence of cold temperatures. In the tropics the fruit keeps a green to green with yellow stains color. Choose oranges that are firm and heavy for size. Blood Oranges may have a full-colored blush or have no blush at all.  Avoid blemishes and shriveled or moldy spots. For the juiciest, sweetest fruit, look for oranges with a sweet, clean fragrance. You can store oranges at cool room temperature for one week or for two weeks in the refrigerator

To determine ripeness of oranges and all other citrus fruit in order to pick them from the tree, the following indices of maturity are known:
The best indices of maturity for citrus are Brix, acid content, and the Brix/acid ratio. External color is a function of climate more than ripeness, and is a poor indicator of maturity. Legal maturity standards are enforced in major citrus regions.  

For more information on oranges (citrus fruit) click here.

Tangerines

Some of the best tangerines can easily be selected in the store because they have a strong and sweet smell. If you find such tangerines buy them, you will not be disappointed.

For more information on tangerines click here.

Watermelons

Unlike other melon-types watermelon can't be chosen for its smell. The only way to pick a ripe watermelon at your store is to do the flat hand test: Tap the melon with your flat hand. If the sound is deep and thick you probably have found a ripe and sweet fruit.

For more information on melons click here.