I would say that if you are thinking about sewing some trousers (or pants as they are referred in the other side of the pond.) I got some information to help you.
I can tell you it ait that complicated as It looks like and once you can find the perfect fit, they will multiply on your wardrobe. Trousers are only 3 pieces- 2 legs and waistband/facing. Requires a zipper so should need to be able to do one too.
First, you need to decide if you would rather destroy ( up pick) an old pair ,that fits and love but it is bit worn out and copy , design your own pattern or buy a pattern and do the necessary adjustments
If you decided do unpick exiting trousers, keep in mind that you need to keep one leg as reference.
The order of sewing is simple: Darts, crotch, side seams, zipper, waist band, and hem!
you do your basic preparations: Wash
and dry your fabric as per the care instructions that are usually found on the bolt of fabric purchased at the store. This prevents the fabric from shrinking
Lay out fabric: Match the selvage ends and smooth out any wrinkles.
Place your pattern on the grain line, and cut, mark all notches and darts
Quick tip for marking: Snip-mark edges: Cut off notches and snip only ¼ inc into edge. Where do I mark? Top of the darts, seam line, pattern notches. I also love using the carbon/tracing wheel combo to mark darts.
Sew all the tucks or darts and PRESS
Line up the sides of front and back pieces, right sides facing in
Pin the two pieces of fabric together and sew crotch seam starting 1 ½ from inseam to zipper opening circle. Sew back crotch seam beginning 1 ½ from inseam up to waist (clip to release on the curves) Press crotch seam open.
It’s your personal preference to sew the crotch seam at this time or wait until finish each front separately. I personally sew all now! If desired, sew over stitches to reinforce them (I do)
Sew the side seams. Do this for both legs. Press seam open.
After that you do your zipper, than attach the waistband to the top of the pants, right sides of the fabric facing each other. Stitch on. Fold up the waistband and press seams up towards the waistband. (You can strengthen the waist area with some interfacing and topstitch.)
Press as you sew MUST be your mantra in every garment. It will make it looks very professional and avoid further errors you only notice once its too late.
On your trousers, when pressing darts:
Press darts flat 1st to flatten fold line and eliminate puckered stitching
Than press darts towards centre over a pressing ham that matches the curve of the dart.( I am writing a post of sewing tools and this will be covered ok!)
Flatten dart, especially point area, with a wood clapper and hold down firmly.
To press your seam in a professional way, press them flat just as it was stitched, them press open over a seam roll (looks like an arm) or a curved ham.
How to hem your trousers?
Wear the pair of shoes that you plan on wearing with the pants and use a full length mirror to get the best idea of what the end result will look like.
Pin the hem in place at the top and bottom.
Insert one pin first along the top of your hem.
Make sure the fabric is straight before you insert your second pin at the bottom If its right, take off the pants and carefully turn them inside out without disturbing your pins.
With your measuring tape, find the length from the bottom fold to the top edge of the fabric that you folded up and inside the leg.
Use this measurement to fold and pin the rest of the hem. Measure in at least in four places all the way around to make sure it is even. Use chalk to mark each measurement.
Measure, fold and pin the other leg in the same manner and press all the way around the bottom edge, removing your pins as you go. Repeat with the other leg.
If hand sewing: Thread a medium-sized needle. Begin stitching a straight stitch 1/8 inch from the top of the hem and go all the way round. Do not sew around the bottom of the hem.
If machine sewing: Use small to medium straight stitch. Begin stitching 1/8 inch from the top of the hem and go all the way round.
If you really need alterations guidance I can recommend this great book called “Pants for Real People, by Pati Palmer & Marta Alto.
happy sewing !