If you're just starting/learning then you're probably best to start with cotton or a cotton blend. If using pure cotton, don't forget to pre-shrink, as it's not always done at the mill. These fabrics are stable (don't stretch all over the place) and non-slip, so you will have the least hassles cutting and sewing with them. They are also pretty comfortable to wear. Their main advantage though is that they are the closest to period-accurate (50's-ish) fabrics, so you'll get closer to the crisp lines and structure of that time.
For added comfort and form-fitting garments (think wiggle dresses without rigid undergarments), you're looking at fabric with some stretch. Not as much as knits (like t-shirt fabric) - just something with added spandex. As little as 2% spandex makes a HUGE difference! It's also pretty easy to cut out and sew, but you'll need to practice a bit with the stretch factor so that you get a garment that is both fitted and that you can still get into!
This is where I would start; the ladies who do this for a living will be able to give you a better idea of what to look for specifically for pinup clothes. Good luck and have fun!
Cotton and poly cotton are great choices. The thing that should guide you is what it says on the pattern packet! That is assuming you are using patterns, which I would recommend for a beginner. Usually they list several types of suitable fabrics that are quite easy to obtain. Most of my patterns seem to have cotton fabrics as suggestions, so go for it!
Totally agree with both of these ladies, to start with get a 2-4 hour easy beginner make while you get used to manipulating the fabric in your sewing machine, cutting, putting pattern pieces together and all that.
See if you can get a family member or friend to help too! I learnt to sew with my mum at the kitchen table and at uni we used to have sewing nights at the beginning of the week to make something for the end of the week
Start with a woven cotton or cotton blend. Stay the heck away from silky-textured fabrics or you'll end up cussing and want to break your machine. :)
Make sure you have nice dressmaker's shears for cutting. It really helps. I suggest getting some Ginghers when you can find them on sale.
And yes- definitely prewash and preshrink your washable fabrics!! I throw mine in the wash on hot and put it in the dryer after- 2 things I never do to any garments. Prewashing takes out the sizing and excess dye, and prevents potential accidental shrinking catastrophes in the future for your finished project.
Good luck and happy sewing!
in the past when I've deviated from the fabric suggestions on the pattern and made something with a heavier or lighter fabric then reccomended- the result was not wearable.