Skills

Skills define the abilities of your pilots and their performance on the battlefield. Of note is the fact that the game forces you to specialize: A pilot can only have two primary skills (granted at level 5) and one specialized skill (level 8).

Skills
Each skill has its own area of focus:
 * Gunnery is universally useful for any 'Mech that uses ranged weapons, but wasted on melee builds. Dump builds in like there's no tomorrow.
 * Piloting is mostly about punching enemy 'Mechs - it does not affect the 'Mech's speed or turning rate. However, the sprinting bonuses, increased evasion, and stability make it a worthwhile investment at least to the unsteady threshold. Light 'Mechs rely on movement, so they should get at least the sprint distance bonus.
 * Guts determine your pilot's survival chance and the added abilities greatly increase your ability to survive on the battlefield. Recommended investment for any pilot assigned to heavy and assault 'Mechs (or any other that's expected to take a beating).
 * Tactics is a varied skill that gives a variety of bonuses, primarily aimed at improving indirect fire accuracy (for artillery 'Mechs), reducing the minimum range penalty (increasing 'Mech flexibility), and most importantly, called shots mastery, which make precision strikes that much more useful.

Depending on which specialized skill (level 8) and which primary skill (level 5) a pilot has selected determines the pilot's title. This is purely cosmetic, and has no function on gameplay; though it can still be useful, as it clues in what skills an enemy has and may help you guess at their tactics and underlying statistics.

Skill-based abilities
The following abilities are derived from skills and unlocked at level five and eight respectively. A pilot can only have two primary skills (level 5) and one master skill. Each skill has an application in the world of Battletech:
 * Multi-Target is excellent for reducing evasion on multiple targets, finishing enemies off, or engaging multiple targets at various weapon ranges. It maximizes the combat efficiency of 'Mechs with multiple weapons, especially if they have multiple ranges. However, 'Mechs with short-range weapons or just one with an extended range won't benefit from it - unless by some miracle, the AI decides to crowd in at close ranges within the firing arc.
 * Breaching Shot is the sniper skill. For obvious reasons, it works best with hard-hitting single weapons (think PPC, AC/20, LRM20, etc.). It also synergizes with Multi-Target if you fire single weapons at individual targets.
 * Sure Footing is excellent, especially for light 'Mechs and others that are expected to cross the battlefield and get shot at. However, artillery 'Mechs and those focusing on tanking damage will benefit more from Bulwark (Guts) and may not want to take it.
 * Ace Pilot is always useful, particularly on light 'Mechs. Shoot, then move? The enemy will hate you.
 * Bulwark is the heavy and assault 'Mech skill, allowing them to easily absorb incoming damage and effectively defend. Not recommended for light 'Mechs and other designs who rely on not getting hit in the first place.
 * Coolant Vent is for the close-combat specialists that cannot afford to exit the fight to cool off, or for those 'Mechs that want to alpha-strike twice in a row. Great for sustained damage output.
 * Sensor Lock is a recon skill for spotter 'Mechs; reduces evasion points, exposes the target, and gives a target to LRM platforms. It also lowers the target's accuracy for a round. However, you can't sensor lock and shoot in the same turn, and sensor range is limited. For these reasons, it is a poor addition to fire support 'Mechs.
 * Master Tactician is at least somewhat useful for most all 'Mechs, but other options may be more useful depending on a pilot's role. However, for all assault 'Mech lances that are anticipating engaging heavy and assault 'Mechs, this skill truly comes into its own: Either your assault 'Mechs will be engaging heavies on a level playing field (because both sides are firing in the same phase) or your assault 'Mechs will be able to get in full opening salvos completely unopposed (significant potential for enemy 'Mechs being destroyed or losing weapons before they can even open fire).

Traits
Traits are additional passive perks received while upgrading your skill line. Of all the bonuses, Called Shots are the most useful for any pilot, greatly increasing your ability to hit enemy parts (especially when used with Precision Strike).

Strategy
You are forced to specialize as you can only have 2 first-level and one second-level abilities. However, you still gain bonuses and traits by increasing the other skills to 5 or more, even if you do not gain the ability.

The various combinations of skills have various strengths:

Gunnery + Piloting is a flexible option for fast 'Mechs. You get bonuses to both ranged and melee damage, along with extra evasion. Prioritizing Piloting is probably better as you get the benefit of Ace Pilot, making you very irritating in a relatively lighter 'Mech by firing then retreating into cover.

Gunnery + Guts is a powerful option for 'Mechs that are planning to stand still and fire, like heavier medium-range 'Mechs. Prioritizing Guts is probably stronger to get Coolant Vent, as Breaching Shot is less useful if you are too hot to fire.

Gunnery + Tactics is perfect for long-range fire, as the indirect fire, minimum range, and Called Shot bonuses synergize well with accurate LRMs, PPCs and so on. On the other hand, it does little for your defenses, so staying at range is wise. Emphasizing Gunnery to get Breaching Shot is recommended, though you could also use Master Tactician to make sure your heavy weapons get in early each round.

Piloting + Guts is good for brawler-type 'Mechs who are mainly close-combat focused, as Coolant Vent works very well in keeping your 'Mech firing after you've sprinted into short range. Once you are overheating, simply melee an enemy for a turn to cool off. Conversely, Ace Pilot could allow a 'Mech to hit-and-fade while being very defensive against incoming attacks during the approach and exit.

Piloting + Tactics synergize best for lighter 'Mechs and can make a solid "spotter" build when paired with a fast 'Mech. Use jump jets to fly around the map and Sensor Lock any enemy 'Mechs just out of range of your LRM or 'sniper' 'Mechs. Additionally, use Ace Pilot to hit and run or Master Tactician to ensure your 'Mech always moves first.

Guts + Tactics is good for making a tanky mid-range fire support 'Mech that wants to sit still in cover and alpha-strike at a single target each turn over and over. Get Coolant Vent to keep firing longer, or get Master Tactician to fire earlier each round.