In Smite there is an achievement for getting 20 kills and 1 death in a single game.
Which gods, general strategy and game mode should I use to maximise my chances of obtaining this achievement?
I am by no means a great player but I've managed to get 20:1 KD or better multiple times. Here are a few tips that may help:
As far as I'm concerned, this is the most important piece of advice I can give. It's certainly possible to get the achievement playing solo, but it would rely on you getting randomly matched with a good team and against a bad team. If you play with friends who are any good, you don't have to rely on matchmaking for your own team (of course, some MM luck is still good when it comes to the other team). Even if your friends aren't great players, being on some kind of voice chat will give you an edge over a group of rando's.
Teamwork will go a long way in helping you get this. Having teammates playing support type gods will help you stay alive to do your damage. You might even specifically plan god combos with them. Friends may refrain from last hitting a retreating player if both of you are in range, strangers probably won't. The first time I got this achievement, I hit 20:1 KD very near the end of the game, and the friends I was playing with told me to just sit in the fountain until the end. If I had been playing with a random group they probably wouldn't have been cool with that.
I would definitely recommend Arena if you're specifically going for this achievement. This mode is more focused on getting kills than any other mode, and the respawn timers are shorter. The short respawn timer is not important for you because you're relying on dying at most once, but you want your enemies to respawn quickly so you can keep killing them.
Conquest and Siege tend to be more focused on strategy, where objectives are much more important than kills, plus larger maps and longer respawn times means more time between encounters.
Assault is probably the least suited to going for this, you can't plan your god picks, plus you have to die to buy items.
Joust has fewer players, meaning you have to draw the game out longer to get the number of kills you need. The longer you draw out the game, the more likely you are to die.
If you just don't like playing Arena, Clash may work. There is a little less of a focus on objectives, plus the map is smaller and the respawn timers are shorter so there are more encounters/team fights.
I'm a little hesitant to recommend a specific strategy, because there are multiple ways to go about this and this may not fit your play style at all. However, I feel like I should include this as it's what I've had success with and I feel like most players can find a way to make it work for them.
This basic strategy involves picking a high damage, item-dependent character AKA a 'carry' (probably a hunter or assassin), and building almost pure damage with little or no defensive items (specific build will of course depend on the specific god). If you can get some early kills and get ahead right away it will be really hard for anyone on the other team to catch up with you.
You'll be super squishy, so you'll probably want to pick a god with a good escape. Be opportunistic, try not to get into a boxing match if you aren't sure you can win. If you drop below half health, retreat! Remember how squishy you are, half of your health could be just one or two good hits. If the other team has any hard CC, get Purification right away. You might also want to get Sprint to help get out of bad situations in case your escape is on cooldown. Don't be afraid to use your ultimate as an escape (if applicable). A lot of people are hesitant to use their ult if it won't get them a kill, but you need all the survivability you can get.
You need a good team to help you stay alive. Hopefully someone else picked a guardian, stick with them as much as possible. In general, never be alone, getting caught by yourself is the fastest way to die. It's also very helpful to have teammates with good crowd control to help set up easy kills.
I'm best at playing hunters, so most of the time I've done this I was playing as Rama or Neith. They both have good damage and an escape that helps ensure that they can stay at arms length. I've also managed to do this with Arachne, picking off lone players and using her ult exclusively as an escape after getting a kill. Of course, these are all single target gods, another valid strategy is to go for a mage with good area damage. This would work best with someone to help get the enemy team all bunched up (like Ares or Hades for example). Mages aren't really my specialty however so I don't have any more specific advice there.
Just remember, this strategy can be countered fairly easily. If the other team isn't prepared for you you'll clean up, but if they are you'll get shut down fast.
What I mean here is don't focus on this achievement too much. Unless you put a group together and you all agree to just farm achievements for each other, it can get really frustrating playing with people who are focused on a specific achievement, it can really make the game less fun. Don't sabotage your team's chances at winning just for a chance at this unless you are sure they are completely cool with it.
No matter what strategy you choose, it's not going to work all the time. You're going to get matched against better players than you, or the other team will just pick gods that shut you down completely. Don't get discouraged by this, and just be prepared to stop going for the achievement as soon as it's apparent that it's not going to happen. Play to have fun first, if you're primary goal is a difficult achievement you're setting yourself up for disappointment.
One last thing: don't even try to do this on a free gem weekend. Everyone has their 'try-hard' pants on and you're more likely to run into pre-made teams.