Every game i play i pick up very quickly and it naturally becomes easier, the only game i ever took a while to get accustomed to was DCUO,because id never played an MMO before.
This game however, is driving me nuts. I dont know what it is specifically, the concepts behind the combat is relatively simple i suppose, but everytime i get into a match, im pitted against level 30`s and just get beasted for 5 or so minutes. I finish up rarely positive in kills and try to focus on objective because its the main way i can get points.
Even 1 vs 1, i often feel like even if i get the first hit, im going to end up getting beasted by some hades guy with a ridiculously OP purple blast that juggles me for what feels like an eternity.
This game seriously needs a better system for breaking out of juggles too, because right now it has become infuriating being juggled.
But yeah, any general tips for holding my own in MP, most of the time if i get a guy to low health in a fair 1 vs 1, he runs away and then his team destroy me in less than a second.
Im about level 29 now (running objectives throughout the day) and an Ares character, i was wearing battle armour (Rank 3) but now ive switched to Rank 1 War armour because it seems to be more balanced with defense and physical power. My magic is Ares Inferno i think ( the one that shoots you in the sky), item is the restoration one, i was using call to arms but figured getting health back is better and then my relic is the Relic of triumph, which i keep subbing for relic of harmony to benefit the team.
I seem to be able to do ok against other ares characters, but get beasted by everyone else because of shields, OP lightning attacks and various other things.
Try using your own shield as an Item. If it blows up on someone, they take elemental damage AND are "burned" for a short time, ticking down their health even further. It's very useful, as is Call to Arms.
If you use a hammer, try to remember to hold  to "charge" it. That'll infuse it with fire for the same burn effect if your next attack lands.
Unfortunately, many players use Elemental builds, where their magic is a main means of offense. Ares cannot live through an Elemental onslaught without at least 1 piece of Medusa armor. Ares is by FAR the most difficult God to use. But once you learn his ins and outs, he can be beastly.
This game takes awhile to learn. You've gotta get a feel for what can be blocked, parried, or evaded, and USE THOSE TOOLS or you're gonna die in a hurry. Also, on offense, learning the timing of all your attacks as well as the range is KEY to being successful. Just keep at it...you'll learn. But remember, many players have a head start on you and that head start has yielded quite an advantage as far as getting used to the combat system.