Specialized Units (UFO2000)
Soldier Specialties
Like in the original games your soldiers will usually have different stats, depending on how specialized your squad is. It is also quite possible to give the same stats to everyone, making it a lot easier to know what they can do.
Get acquainted with your soldiers
Either having a lot of different specialties or a single one, the most important thing to do is to memorize what each unit can do and what it cannot. For instance a soldier with a 50 throwing skill (the basic) will most likely miss if he throws a grenade. And if he throws it while between buildings there's a good chance it will hit the wall and blow right in front of him. Or, a soldier with 50 reactions will most likely not fire immediately at an enemy that steps into his vision, if he had spent TUs already. Or, a soldier with 80 TUs needs 36% of them to auto fire his laser rifle as it is advancing for a close range kill; otherwise you just made the enemy's task a lot easier! These are just a few examples of mistakes that can happen when players don't know what their units are capable of. If you know what they can/cannot do you will prevent easy kills for the enemy or fratricide kills.
Common stats vs. specialized stats
It is easier to prevent mistakes like those described above if you keep the number of specialties low, helping you to memorize faster the capabilities of your units. One basic configuration is increasing the firing ability to 80 and split the remaining points between the other stats. This however might make you vulnerable to a more specialized enemy (he also has weaknesses on his units but they don't apply to his entire squad). The old adage always applies for both cases: prevent him from taking advantage of your weaknesses and maximize your strengths.
Examples of specialized units
Rifleman
Rifleman should compose the largest group inside your squad. They should have maximum firing accuracy (80 points) and be armed with accurate weapons. The remaining points can either be used for TUs, Stamina, and Health or to create the subcategories of Snipers/Heavy Weapons.
Sniper
Snipers have high firing ability and reactions. They should carry a powerful weapon capable to taking out an enemy with a single shot. While Snipers can be very effective in some situations they are very vulnerable (for more info see section 13. Reactions: do's and don'ts)
Heavy Weapons
Heavy Weapons units have their Strength stat increased to be able to carry the ammo for Cannons/Launchers, in addition to the Firing Accuracy stat. However this might not be necessary if the game is played with the Ground Option activated or if another squad member carries the reloads.
Scout
These guys are your eyes. A Scout should have 2 characteristics: to be able to move a lot (high TUs/Stamina) and to survive. For the last characteristic it can either have its Health increased/use armor or you can simply have several unarmored scouts (the original game's 'rookie fodder' tactic).
Grenadier/Demolitions
These units usually require high Throwing Ability but sometimes that might not be necessary, if you only are using grenades to make smoke curtains on the open or if you're using them to booby trap buildings (check chapter 5.2.2. Explosive tricks).
Assault
This is a very specialized unit that can move and engage at close/medium range. On the original game it would be a soldier with high TUs, Firing Accuracy, Stamina and Reactions (and all of the other stats, basically), to be used while clearing UFOs. On UFO2000 however it is not possible to increase all these stats to their maximums, so a compromise will have to be made between the stats.
Of course, other specializations are quite possible, depending on a player's tactics. One helpful element in specialization though is to have secondary specialties assigned to a soldier. For instance, a Heavy Weapons can grab a rifle and act as a Rifleman/Sniper or an Assault unit might be used as a Scout. It might not be their appropriate roles, but necessity is the mother of all inventions :)