The following guide aims to summarize Anthem's loadout core mechanics, without going into the details of specific builds. Its goal is to explain those general concepts that are useful for all Javelin classes to build effective loadouts and help you understand how to best outfit each of your Javelins to the playstyle you prefer.
Anything with a gear icon only affects the item that holds the inscription. For simplicity, I call them "own" and group them accordingly. E.g. "own damage" inscriptions come in various flavors, which are all equivalent and therefore not distinguished here.
A Javelin icon means the effect applies to everything, not just that specific item. This is usually referred to as "Jav wide".
Inscriptions are randomized item attributes that come in two main groups: Primaries provide direct combat boosts, such as damage and armor, while secondaries are of a more indirect and supportive nature. Since universal armor components hold a pair of primary inscriptions, they are often superior to class specific components, that come with a pair of secondaries instead. All other items have four inscriptions each (primaries at the top left and bottom right, secondaries at the top right and bottom left). Perks are situational bonus effects found on all Masterwork and Legendary items. Certain perks of class specific armor components are useful enough to be part of most builds for their class.
When preparing for a mission, pilots can equip sigils, craftable items for single use, that grant a bonus during that mission. While this is optional, it can be an integral part of a build. Universally useful sigil effects include Combo Damage, Ultimate Damage and Heat Capacity.
Many javelin builds revolve around cycling certain attack patterns, such as various combo primers and detonators. Inscriptions for extra charges and recharge speed can greatly improve the flow of these attack cycles, but this really depends on each particular gear piece. Some gear takes a while to aim and fire - in this case, having an extra charge allows to recharge the gear already while firing the next shot, which can be an enormous advantage. Gear with multiple charges is generally recommended, while additional recharge speed is often a matter of personal preference.
As of version 1.7.0, the highest gear score of items is level 80. The average gear score (AGS) of all twelve loadout items is used to scale the damage of certain attacks: Ultimates, combos and ticks from fire, electric and (Interceptor) aura ticks. The damage scaling of these attacks is exponential and doubles with every ten levels of the AGS. But why is this important? Because the damage of weapons and gear does not scale in the same manner. In particular, the gear score of legendary items is higher than their increase in base damage, resulting in a much greater boost of those attacks scaled by AGS. For that reason, many builds heavily rely on exactly these damage sources. In order to maximize the AGS scaling, it is not necessary to use twelve level 80 items: The loadout can include one level 75 item and still yield a rounded AGS of 80.
In Anthem, there are many different damage boosters that stack additively. For instance, if a weapon comes with a local damage bonus of +400% damage, and certain abilities and perks add a total of +300% weapon damage, then that's already a factor of 8.0 overall. Now, if we add another 30% damage from an inscription or sigil for an overall damage factor of 8.3 on that weapon, we cannot expect to see a big difference. The same 30% extra damage will be significant, though, if we consider something like fire effect ticks, that have few or no other damage boosters on them. If anything boosts damage by a certain percentage, you can always assume additive stacking like this.
Additive stacking is also relevant for melee damage. There are various perks that grant a considerable melee boost, for instance from the universal component Bloodlust. And having a Colossus with Berserker's Cry in your squad adds another occasional +200% to the stack. The Interceptor is the only class that can effectively leverage melee damage with fast attack patterns, however, the melee boosts will be irrelevant whenever the ultimate is active. Other classes will mostly use melee to trigger perks and combo cycles, so melee boosts are of limited value for them.
While damage percentages are added to form a damage factor, there are also other factors that will stack multiplicatively. The exponential AGS scaling mentioned earlier is one such factor. Other examples are damage type factors against shielded and armored enemies, hit zone multipliers for weak points, and resistance debuffs (from acid effects and target beacons or battle cries). The point is, that the product of these combined damage factors will have much a greater impact than maxing a single multiplier while ignoring the others. In practice, this means that you will always want to take advantage from effects like acid, especially when playing solo.
So far, we stated that those attacks scaled by AGS have a high damage potential, especially when boosted by other damage factors. In this context, it is important to know that +Dmg inscriptions do improve effect damage ticks, but they have no use on ultimates and combos. Ultimates have their exclusive damage inscription, and for combos, things are more complicated: The Ranger and Colossus can scale them with Combo Blast and Combo Impact inscriptions, respectively, while the Interceptor and Storm have no inscriptions for combo damage. But there is something else. Some items have situational perks that increase all damage. Unlike the +Dmg inscriptions, these damage boosters are truly universal. That's why items like Symbiotic Surge, Shock Treatment, Rampager or Way of Integration are so useful, as they also boost ultimate and combo damage.
High damage outputs are a wonderful thing, but a downed Javelin is not any good to leverage them. So, a pilot should either avoid taking damage or maintain a sufficient repair rate. Special perks that restore armor can be tremendously useful for this, but repair drops from defeated enemies can work just fine. Both, Resupply and Repair Drop Rate inscriptions will yield more repair packs per enemy, which in return trigger the damage perk of Symbiotic Surge. This universal armor component is used in most builds, and keeping its perk active is a good reason to invest in said inscriptions. Ammo Drop Rate is less important, although it can be used to avoid reload times, and serves for repair with the Rejuvenating Ammo component.
Some items grant situational damage resistances, such as Softened Blows, Feedback Loop, Airborn Advantage, Vanguard Token or Blades of Warding. While partial resistances are powerful on their own, stacking two such perks can make a javelin completely invulnerable. There are also inscriptions and sigils that grant minor resistances, but these are only really useful on top of an active resistance perk. Some of these perks trigger on a shield break, including the universal component Softened Blows. For this reason, Shield Delay inscriptions can help to regain damage resistances more frequently. These perks are rarely used by Colossus pilots, because their shields usually do not break. Having a Colossus with Shield Pulse in your squad is another great way to stack up your resistances.
Armor inscriptions provide significant boosts to a Javalin's durability, but stacking them will be much less effective than taking advantage of resistances and repair. A general recommendation is to gear up around +180% Armor, which can be done already with a single weapon or universal component. Running a javelin with less armor is well possible, but increases the chance of getting downed by single hit. Inscriptions that increase the overall shield capacity and refresh rate are generally much less effective than armor inscriptions.
Some builds are centered around using a Javelin's ultimate, which becomes available whenever 100 charges are accumulated. These charges are gained mostly from combos and certain item perks, which are core items of some ultimate builds. Additionally, the ultimate recharges passively over time, and this rate can be accelerated with inscriptions on class specific armor components. The most relevant component for ultimates, though, is Emergency Power. Its perk triggers on low armor and refills ultimate charges instantly, but at most once in two minutes. The universal component comes with a fixed +30% ultimate damage, and potentially more of that from inscriptions.