I think using references is definitely a good idea.
Also, I may have misinterpreted what you've said, but it sounds to me like you focus on one eye first and then go to the next one; it might be a good idea to build up a face or a figure gradually, only going into detail when you have a pretty good idea what the face is gonna look like.
If you're using traditional medium, keep it light - you will be doing a lot of adjustments. If the work is traditional, look at your work in the mirror - if it looks off, something isn't working. If you're doing it digitally, just flip it horizontally. Remember to step back and look at it from afar.
As far as figure goes, knowing your anatomy will help. Get a good anatomy book or look for references online. Life drawing helps, but if you don't have access to that, references is the next best thing.
If your goal is to get better at figure drawing, don't focus on detail. Rather pay attention to big shapes, direction, silhouette and proportion. Don't over-complicate it for yourself - simplify the shapes you see, at least in the first stages of building a figure.
For an eye tutorial, this is what came to my mind first, but even Linda said not to get into details too soon: [link]
Anyway, these are some thought, hopefully you'll find some of it helpful. Keep up the good work!
If you really want to improve then don't draw anything without a reference so you can get you hand skills working well.
I think one thing that can help you most is drawing just a silhouettes of people in poses. That will help you see and improve on proportions and drawing shapes. Then later they will be an easy memory of poses because your mind remembers them like learning you ABC's.
Just imagining the poses in a silhouette, helps you remember poses.
Silhouettes don't help much if they are shapes of loose fitting clothing like a woman with an over coat, a cape or shawl, because you don't get much of the shape of the anatomy like to do of a girl in a bikini.
Silhouettes also make it easier to drawing the anatomy of different animals.
Most people spend a lot of time leaning the bones and too much information that artist don't need. Artist only need to study forms, shading and textures on the outside of the body.
You have a long ways to go, but when you get most of the anatomy start working on drawing from motion. When you draw one pose from a body not standing still, then you remember all the actions and details that can last decades in creating any anatomy. The more details you get in that one pose is added to the constant movements of the joints being stored in your memory and watching those details repeat the action.
At your current skill level, I would recommend always using references if you are not already doing so. If you are painting a straight face i.e looking back at you directly, you can always duplicate one of the eyes you already drew and flip it horizontally.
This is probably one of if not the best tutorial on eyes [link]. It should help you a lot.
Remember, when painting portraits the eyes are the key. If they suck then the rest of the portrait might as well suck too. Pay attention to the little details, work on a large canvas and most importantly be very patient. Start with a sketch of the face to make sure you have the right proportions and anatomy before you start expending any effort on painting.
I would recommend always using references if you are not already doing so. If you are painting a straight face i.e looking back at you directly, you can always duplicate one of the eyes you already drew and flip it horizontally.
Sometimes when I do that I just go over the duplicated eye and screw it up a little so it doesn't look perfectly symetric It's a good technique when you're lazy or in a hurry, but I don't doubt that drawing them both from scratch is the best.
This is one of your thumbnails....looks like what I said would work just perfect when you duplicate on eye and flip it horizontally i.e like a mirror not e-e. It was offered as an easy help in case he ever wants to use it as a shortcut.