Probably the number one question that knitters ask me, is how to tighten up the last double-stitch when working German-Short-Rows in the round. This final turning point from the last short row - the last double-stitch to be worked when starting knitting in the round again - is slightly turned to the other side and ends up big and funny looking when it's knit as usual.

Insert the right needle (or an extra DPN needle if it's easier to handle) into the right leg of the stitch, that is positioned 2 rows below the first stitch on the left needle (as shown above)...

Work like this towards the left, stitch for stitch and carefully move the extra yarn from one stitch to the other and let the yarn travel to the side in this way. The idea here is to try to pull out a tiny bit less excess while working each stitch, so that your pulled-out loop gets smaller each time because every stitch "absorbs" a small fraction of the excess until it is all gone. You don't want to end up with all the length on the left side of your double-stitch and just transport the huge stitch itself from one side to the other. 
What you need is to have this extra loop of yarn distributed all over the 3-5 stitches towards the left, or until it isn't visible anymore (it doesn't need to look perfect at this stage).

On the picture on the right, where I have continued knitting about 4 stitches more, you can see clearly that the big double-stitch has been transformed into a normal sized stitch, while the extra length of yarn has been "incorporated" into the smaller stitches to the left, making those stitches larger in size and the difference between all of them less pronounced.

There are other methods where you are working this last short row stitch differently as the others before, to "make it behave" (sometimes by knitting each leg of the ds together with other stitches, for example).
I am personally not a big fan of this idea - even if it might be quicker to work.  It can distort the stitch more if not done right, make the fabric pull in at that point instead of letting the natural flow of the stitches open up during blocking, leave the smaller stitches in their tiny misery or add bulk to a section where we want to keep things nice and flat.

2. Eliminating larger stitches, even after having completed the project:
Good news is that you can manually repair the tension to get rid of all big, distorted stitches in your knitting - not only the short row double stitches discussed here - but also when you have strange laddering going on in magic loop knitting, strange holes near the underarm cast-on in top down knitting or the occasional giant stitch making an appearance.
If you already have finished and blocked your project and you still want to get rid of any stitch that looks too big, or if you still find that the above tip didn't yield a perfect result, even after blocking, this "Post-Production" process will surely be of interest:

You will need a smaller sized needle, good lighting and some patience to make this work:

I find that we knitters sometimes forget that we are just working with sticks and a long length of string, which makes up a fabric of interlocked loops. A fabric that one can influence at any given time by shifting the amount of length in the finished surface - during but also after knitting.
This fact actually opened up a whole new way of thinking to me; on how to handle my knitted fabric and to understand a lot of things about the flow of the stitches in knitting.

As I said the logic behind all of this is really simple - too simple maybe and not at all dramatic - but it does the trick every time: With just a little patience and an even tension, all "non-conform" stitches, ugly double-stitches or other unwanted distortions in our knitting can be successfully remedied and persuaded into shape.

I am sure that this isn't the only way to eliminate this kind of problematic stitches - it is the way I prefer for years now and I am very happy with it because it allows me the freedom to repair any unevenness that might have escaped me during knitting.
But maybe you have another method that works better for you?

... our crafts-teacher showed us a very cool and simple method for a looser long-tail cast on. 
It allows you to work the first row easily without fighting to insert your needle in some tightly wound CO stitches .
I just remembered this recently (together with some other not-so-useful school memories) and thought that maybe not everybody is familiar with this easy trick to achieve a friendly start to their knitting. So I thought I'll share this "fond memory" especially for the ones that love the look of the long-tail cast on, but never get it to be elastic enough...

And there you go: The needle that is left inside your knitting is now holding a nice set of loose stitches - that are big, open and stretchy and ready to be worked into.

Apropos circulars: 
If you use long circulars for a smaller project you can "fold" them in half and use the two needle tips as the straight pair above. Just make sure that you don't loose the stitches when you try to get the one needle-tip out of them by pulling on the cord end... for larger projects this might get very fiddly!
You theoretically need a cord that is a little longer than double the length of the casted on stitches to accommodate them when folded in half, so this is why an extra pair of circular needles in the same needle-size would probably be a better idea for a larger project (and much easier to pull out of the CO after it's done).  

This Twin-Needle system is producing a kind of an elongated, oval needle tip and not a round one - so your loop is long while the stitch underneath rests still neat and less bulky  - that's really a detail though and probably too much of information.