Profit

A profit is the amount of resources gained from a raid. For example, if a fleet of 2 Small Cargo Ships attacks a planet at the cost of 26 Deuterium, and steals 1000 deut from the planet, the profit is 974 deut. You can calculate a profit like this: total gain - loss = profit.

For example, if one of the cargos is lost in the raid, you must substract the value of the lost ship to accurately calculate the raid's profit.

Maximizing Profit
Furthermore, to maximize profit it would be a good idea to consider factors such as maximum fleet slots and the size of your total fleet. IF you have few fleet slots and/or a large fleet (especially cargo ships) it will be highly inprofitable to use a whole fleet slot on a single transporter (large or small according to your total fleet size). The result would be a large portion of your fleet not being able to be used as all your fleet slots will be full. A profitable target would thus be a planet with resources enough to justify a raid. And naturally with few enough defenses so you won't waste a lot of deuterium on support fighters.

You should try to keep an average of (total transporters / # of fleet slots) transporters per raid. Below that you don't optimize your fleet slots properly. Find better (larger) targets or upgrade computers. Above that and you should consider increasing your fleet. Obviously this applies mostly to beginning to mid-game. Later on you should focus more on fleet crashing. Also remember as you get more advanced attack ships that they carry cargo as well. Use an attack calculator such as SpeedSim to get a feel of how many ships you need to win a raid, and make sure to not overkill, so you maximize the profit per raid.

Consider the speed of your fleet as a factor as well. The faster the fleet, the more raids per day you can cram in, if you raid more than once a day. Consider raiding undefended planets (especially farming of inactive players) with small transporters. Since they are significantly faster than the large, you can raid more with those a day too. The main downside to small transporters though, are that they don't last in an attack with just a medium defense, because they are basically cannon fodder. The lack of shield and structure points make them unsuited for raiding more than lightly defended planets. And in that case you will probably need more attack ships to keep the loss of ST down than you would if using LT.

Fleetcrashing
Fleetcrashing is by many if not all professional OGamers considered the ultimate way to make a profit. The reasons for this are (amongst many): Some weighty reasons to start fleetcrashing. But when fleetcrashing for profit consider the following:
 * You get all the resources in one run (if you have the recyclers needed)
 * Since you send the recyclers to the debris field they don't enter combat as such. That means you needn't overkill to avoid losing too many transporters. Thus you don't waste as much deuterium as you would by raiding the same defense.
 * Most (semi)professional players invest their resources in their fleet. As such they build up more resources in their fleet than is available to raid on their planets.
 * Inexperienced players sometimes invest tenaciously in fleet, while lacking investment in the defense to back it up.
 * Inexperienced players may forget to fleetsave or forget to check up on a fleetsave.
 * Even if you do fleetsave, it may be possible to phalanx it, if the fleetsave is not done properly
 * Speed. Recyclers are only half the speed of large transporters. So if you want to crash a fleet make sure you can collect twice the amount as you can by a raid. Since they are twice as slow as raiding (approximately).
 * Make sure the planet has a debris field so you can send the recyclers in advance. If no DF is present attack with a spy probe first, then send in the recyclers. Calculate the amount you will need by using speedsim or similar. That way you can wait and send in the fleet later, thus minimizing the windows of opportunity your opponent has to react to you attack. He can't detect the recyclers (though most experienced players know to expect an attack in case of a probe crash).
 * When fleetcrashing a heavily defended planet it may not be profitable, similar to raids. Consider the gain - expense compared to the fleet slot or the alternative lightly defended planets.
 * Remember fleetcrashing does not earn you any deuterium. So if low on that you should be raiding select targets instead.

Resource Looting
Also remember that deuterium is more valuable than crystal and crystal than metal. Even though they all count equally towards total points, deuterium and crystal are more rare. If you need to choose between targets, make sure to prioritize deuterium, then crystal before metal. The standard calculation is: metal: 1, Crystal: 1.5 and Deuterium: 2.5. So 5000 deuterium is worth 12,500 metal. This is just a rough guideline though, since all resources count towards your score, and supply and demand often even out the differences. Usually you will always find good need for any resource you loot.