The Trunks Saga is one of the shortest arcs in Dragon Ball Z. It covers Mecha Frieza and King Cold's arrival on Earth, their swift defeat by Future Trunks, the warning of the androids and the Z Fighters' training. It's so brief that most people either consider it an extension of the Frieza Saga or the start of the Android Saga. It's kind of sad, but there's a simple fix to this-- extend the fighting.
Trunks easily defeating two of the biggest threats in the series thus far, while awesome, is anticlimactic. If he had a little more trouble, he could have shown how strong he is while still making his opponents out to be credible threats. Furthermore, if Frieza were removed entirely and the focus of the fighting was on King Cold, it could have given one of the most wasted characters in the series a chance to shine. Here's an idea of how the Trunks Saga could have played out if King Cold were given a bigger role.
To get the full sense of King Cold's power, it might be best to remove Frieza from the arc entirely. Technically, nothing about him being here is necessary. If he had stayed dead, King Cold would still feel inclined to go to Earth to punish those who harmed his son. Keeping him dead would also strengthen King Cold's fury and resolve.
Furthermore, omitting Frieza doesn't change the power dynamic of the actual series. In the anime, Mecha Frieza is stated to be stronger than he was on Namek. However, despite this upgrade, King Cold is purportedly even more powerful than his son. However the battle between these two and the Z Fighters was supposed to go, it's clear that King Cold was always going to be the endgame.
As for how King Cold could have been made into a credible threat, that has to do with the pacing of the fight. The Z Fighters could have their shot at the galactic tyrant only to be beaten. Trunks shouldn't arrive until after King Cold has soundly thrashed the rest of the Z Fighters.
Trunks himself should also have to struggle with King Cold. He can still have the upper hand, but the fight shouldn't be as one-sided as it was in the anime. It should be more like Goku's fight with Frieza; even as a Super Saiyan, he still took damage and had to expend a good deal of effort to beat Frieza at 100%. Trunks should have at least that much difficulty fighting King Cold.
Speaking of Goku, the Trunks Saga might also benefit from him showing up. In the anime, Goku could have used Instant Transmission to get to Earth, but he held off when he sensed Trunks handling things. If Trunks were to struggle against King Cold, however, Goku might be inclined to teleport to Earth to help out.
This would be where the real fight begins. Goku and Trunks would have to use all their power to finally put down King Cold fighting at 100%. The galactic tyrant might even have a Final Form like fans have been theorizing. This would keep Super Saiyans at the top of the food chain while finally turning King Cold into the threat he was made out to be in the anime.
After King Cold's defeat, Trunks could finally get to relay his message. He would tell Goku about how King Cold, while strong, is still nothing compared to the coming threat of the androids. The harder the battle with King Cold, the better it contextualizes how dangerous the androids are.
With some minor tweaks, Trunks' arrival could have been so much more than a simple in-between point for the Frieza Saga and the Android Saga. By removing Frieza from the story and making the confrontation with King Cold into an actual fight, there could have been some real tension and drama. It would also finally give King Cold, one of the most underused characters in Dragon Ball, a chance for relevance. The looming threat of the androids could in turn sound all the more menacing. This mini-arc could finally become the actual saga it was meant to be.
