Since I have little to do right now, I'll go in a little detail with a couple of examples.

[hider=Cyra+Bastion+2]
Take someone like Thundercrash's character Cyra for an example. She's a very good tank considering her 2 shields and has high-ranged options with her guns. This leaves her with several weaknesses. First and foremost, according to her sheet, she basically waits for her opponents to come to her, and her offensive prowess is low. Taking both that and her strengths into account, however, makes hatakekuro's character Bastion have good synergy with Cyra. While Cyra has weak offensive prowess, she can lock people down with her machine gun. Bastion has quite a high range on his bow, but it's quite hard to hit with and has limited ammunition. Hence, with Cyra locking down targets with her machine gun, Bastion can pick them off.

Furthermore, he has quite a high agility and can comfortably square off against other speed types with his semblance, hence covering for Cyra's other weakness, her relatively low mobility. While this works quite, they could use something in terms of close range assurances, so either tanderbolt's Tommy or my character Thaddeus may be a good idea in a team like that.[/hider]
[hider=Tommy+Thaddeus+2]
Tommy and Thaddeus are both long-lasting close ranged fighters able to outlast the majority of opponents. They can easily make any skirmish a battle of attrition by turning around and draining the opponent's resources. Tommy and Thaddeus both have an advantage in prolonged fights because of their longetivity. In this case, the synergy isn't so much managing their weaknesses, it's playing on their strengths.

Their lack of ranged power might be fixed with the addition of Nallore's Sienna, who (I assume) is a light damage mobile harasser, peppering foes with bullets to wear them down without getting hit herself (I'm assuming all this. Care to confirm, [@Nallore]?) Combining those three, you get a team composition who can drag out fights for pretty much as long as they feel like.

One important thing to note, however, is that someone like Volenvradica's Lelia wouldn't be good with this team composition because her weakness is prolonged fights.
[/hider]
[hider=Lelia+Solomon+2]
Speaking of Lelia, however, she could go well with your character Solomon. Lelia's specialization is burst damage, so speed is a pretty big factor in her damage. She's very precise, so characters that can initiate a fight and disrupt/separate the enemy team would be ideal. She can actually do this herself, I believe, but for bust squads, you also need someone to help the main damage dealers peel away from the fight if things go hairy. This makes Solomon ideal as his natural tankiness and speed can both help her burst down a few members of an enemy team and also escape without many losses.

The burst team is, however, bad at sustained fights and they are quite vulnerable if they don't take down their targets quickly. If the enemy is prepared for their entry and manage to escape before any real damage is done, it can be hard (but not impossible) to catch them. One possible fix for this is someone like Sienna, who has great mobility because of her hoverboard. While (I assume) she does little damage, she can corral enemies back to her teammates, or Solomon who can, again, pick people off with range. He also fits quite well as he moves quickly and can help with the initial melee burst.
[/hider]

Keep in mind that, with all these synergies, they still have weaknesses. Synergies either work with people's weaknesses or capitalize on their strengths to form a strong team. It's something to be considered as a group of strong individual fighters can be beaten by a team of weaker fighters with better synergies.