Good morning
@Hayley Welcome to the forum.
Clothing alterations is my 'thing'.
Tops...Generally speaking I take them in through the side seams. Depending on the style...(like a shirt/blouse)... and how much needs coming in I might pinch a couple of darts in the back to give a bit more shape.
I've never worked with a pattern to take something in.
Jeans...I suppose you could take them in down the outside leg seams but then you will have a problem with the front pockets. You will be making the pocket openings smaller so you probably won't be able to use them. The waistband in this case would be seamed at the sides to take that in.
Usually when I take jeans or trousers in I will take the amount in down the centre back seam, but two sizes smaller might be too much to pull in at the centre back. The back pockets will be pulled too close to the back seam and look a bit odd. (Although I've done that many times on the insistence of the customer.
)
It all depends...how much needs to be taken in, the style of the garment...I decide what's going to work best when I do a fitting.
You have sewing machines which you have never used? Have a play around on the machines before you do anything. The jeans are going to be tough to stitch through the layers so you'll need a heavier weight needle to go through it all without the needle breaking.
If you have t-shirt, stretchy knit fabrics in your tops, then a ballpoint needle is needed for those.
There's lots of help online nowadays with videos, forums, etc. The GB sewing bee might show some methods of doing things but you'd have to trawl through a lot to get what you were after.
Don't know if I've helped at all but don't be scared to ask.
We're a friendly lot on here, and good for you
for not just throwing your clothes away and buying new.
Pretty much anything can be altered smaller and many things can be made larger too.
Sandra.
xxx