I'm playing KSP for a while now and I once did a trip to Eve and back, learning some stuff on the way. I see a lot of people struggling with Eve return missions and I noticed that I have a few tips that would be helpful for many of those people, so I decided to write a guide about it. If you see any errors in it, feel free to ping me.
Who is this guide for?
Before following this tutorial, you should have already done other manned interplanetary missions (with safe return to Kerbin) and you should be able to put a few hundred tons payload to LKO in a single launch.
You might be able to complete the mission without these mods, but I highly recommend using them since it will make stuff easier.
RCS Build Aid
Kerbal Engineer Redux
Where to start (and where to not start)
The challenging part of the mission will be the journey from Eve's surface back to Kerbin and not the other way. You should begin by designing a vehicle that can get away from Eve's surface. Don't worry about landing on Eve yet. (We'll place parachutes, landing legs and heat shields on decouplers and eject it all after landing on Eve.) For now, just pretend the KSC is located on Eve and you want to design a rocket for a one-way trip to Kerbin (or just to Eve's orbit if you want to do an Apollo style mission). You can do test flights from Eve's surface by teleporting your vessel to Eve using HyperEdit or the cheat menu and hit "Revert Flight" afterwards.
Important: Do not start dealing with how to land on Eve before you're completely sure that your vehicle can get away from Eve, otherwise you'll probably waste time designing a landing system for a ship that doesn't work.
Apollo style makes lander design much easier since you'll have to carry much less mass from Eve's surface to Eve's orbit, but it is possible to do it without Apollo style (I did this myself).
You can refer to the Community Delta-V Map for the delta-V requirements, but the delta-V readouts will not replace a test flight!
The Wiki says the following about rocket engines at low altitudes on Eve:
However, I remember that this was already written on the wiki before the Making History DLC was released, so it could be possible that some engines from this DLC are also well-suited, but I haven't done further research in this direction. I decided to use the Vector engine because my vehicle quickly became quite big and therefore needed a lot of trust and the Vectors are more compact than the Mammoth. Just pick the one that suits your design the most.
For more efficiency you should use asparagus staging.
Feel free to put the capsule under a fairing. You can later attach a command pod at the bottom (on a decoupler) and use crew transfer instead of ladders.
How to land your vehicle on Eve
For landing, we'll need to add a few stuff. Place it on decouplers so that you can dump it before taking off again. RCS Build Aid can display what the touchdown speed will be with the current ammount of parachutes. This may be helpful. Since your design is probably quite big, you'll want to use 10 meter heat shields. You can also clip multiple of them into each other if one isn't big enough.
Large heart shields at the bottom will probably cause your lander to flip around during reentry because they act like a very big parachute and force your ship to face prograde. This will lead to your ship being destroyed by reentry heating. You can compensate this by adding even more heat shields at the top of your vessel. These won't serve as heat shields but they'll stabilize the vessel during reentry. If you still have problems, you can try if a prograde reentry works better since you have heatshields on both prograde and retrograde side.
You'll have to drop the heat shields before touchdown. You may have to experiment a bit until you find a way to safely separate them.
Don't forget to attach the landing legs on decouplers too. Eject them at the moment you ignite the engines for takeoff and you should be fine.