So Farm Mods for those speed secondary stats.
Okay, but if we're giving mod advice, the please, @GegeGerard24 remember that getting a good match between set-bonus, primary, and secondaries is more important than having one outstanding secondary -- even if it's speed.
Early on when you're just trying to boost speed, make sure you're farming speed sets.
Later when you're trying to farm Defence or CritDamage or Potency sets, it's going to be just as important to make sure that you have the right secondaries as to ensure you have a fast speed secondary.
For instance if you have a defence set bonus, then you have to have a Defence% primary or secondary or you should sell it, even if it has speed showing.
Think about it like this: you have only 2 or 3 set bonuses you can acquire, right? Because there are six slots but you don't get the set bonus unless you have 2 or 4 matching set bonuses.
If Defence is important enough to use up one of your 2 or 3 precious set bonuses, then it's important enough to use up one of your 24 total secondary bonuses.
Critical Damage mods should always have CritChance, Offense, and Speed (one of these could be a primary, the others -- or possibly all 3 -- can be secondaries) or you don't want them.
Defence mods should always have Defence% and speed, and you should consider them even better if they also have Protection% or Health% and slightly better if they have +Protection or +Health.
I won't do all the mods here, but think about what you're levelling and slicing up. If something is an offence mod, you want as many offence-related stats as you can get. (This includes Potency for some attackers, but not all.) If something is a defensive mod, you want as many survivability-related stats as you can get. (This might include Tenacity, but doesn't always, so this shouldn't be a requirement, but if you have a mod with lots of good defensive stats and the final stat is Tenacity this is generally better than if the final stat is CC% or something.)
Finally, there are often exceptions to the rules when you are putting together mods for a specific character with an unusual kit.
For instance you might have General Grievous. Since his damage is based on his health and not his offence, you **can** equip him with 6 Health-set mods, but you can also equip him with 4 Critical Damage mods + 2 Health mods. If you do that, though, you'll want Crit Damage mods that have Health secondaries instead of Offense secondaries (though Crit Chance is still good).
It's fine to break the general rules for a specific character with an odd kit. But don't invest in mods that don't follow the general rules just in the hopes that someday CG will release a weird character with just the right custom kit to make that mod work.
Follow the general rules. Collect lots of mods that follow the general rules. Don't break the general rules unless you have a specific character in mind that you're collecting for. You don't have to have Grievous already when you start collecting CritDamage+Health mods for grievous, if that's the way you want to go, but you do have to be aware that you're using those inventory slots specifically for Grievous, and that you only have so many such slots.