If its your first time building, assuming the rest of your equipment is safe, I'd still shoot more for the .5 ohms than the .3 . You'll always want to rebuild and try something new later, so go with the "safer" or at least less extreme build first.
If you're shooting for .5 ohms with a dual coil build, you'll need to wrap two 1 ohm coils. Its hard to tell you how many wraps without knowing what diameter you're wrapping at. So, pick your inner diameter, find a drill bit or screwdriver to wrap around and plug the variables into Steam Engine. This will tell you how many wraps you need on each coil. So wrap, then put them in your RDA
Now, before firing, check your ohms. If you have a regulated device with short protection you can technically (but still shouldn't) skip this step. If you have a mech you REALLY need to check it on an ohm reader first before firing it. A short on a mech will not be fun.
When you check the ohms, supposing you followed the steam engine correctly, you should at least come close to what you were aiming for. Being + or - .1 ohm is OK, but if its really far off of what you were aiming for it means something is wrong. Make sure no wires are shorting against your deck and that your post screws are snug.
Once you've done all this, its time to dry fire the coils. This will serve two purposes. First, it will burn off any oil from the wire which will taste like shit. Second, it will let you see if your coil is heating evenly. It should, like Neunerball said, heat evenly from the middle. If you see that it isn't, get a pair of needle nose pliers (or preferably ceramic tipped tweezers if you have them). Fire the coil, let it glow, RELEASE the firing button and then gently squeeze the coil. Repeat two or three times and your coil should be burning nice and even.
If you have any other questions, ask first. Someone on here is always happy to help, and its better to wait half an hour for an answer than to rush ahead and end up with a problem.