Personally I prefer not to wear cute looking clothes to work, but these didn't even fit. I figure this is a pretty common issue for the ladies, but couldn't find any simple instructions online. (Plus work clothes in women's cuts usually cost way more-- LAAAAAME!) So here you go, buddies!
(This method can be used to take in and adjust just about all clothes. I've done it to take in tshirts, shorts, pants, coats, pants, to make dresses more shapely, to make pants for much taller people fit me well. Don't be scared!)
Step 1: Find Your Size
First, put the pants on inside-out. This way you can see all the seams and get a good idea of how your pants were assembled. The best way to alter clothes is from the seams that already exist. Just pinch the pants into place and safety pin them when you get the shape you want. Be sure they're still comfortable when you sit, bend down, hop a fence, etc. Keep the pins in a line so it's easy to keep track once you're sewing.
The pants I'm altering fit at the waist and butt, but the legs were way too loose and went down too long. So I'd need to first take in the legs and them hem them. When greatly altering jeans, I've had the easiest time and most success from taking in the outside seam. However these ones are triple stitched flat, and since the top part fit well enough I didn't want to try to blend one type of sewing with another and end up with lumps where the stitches meet. Pinching them from the inside pulled the front in a weird direction. So i chose to just create a new seam and take them in from the back of the leg. This isn't how pants are made, and probably isn't how I'd alter fancy pants, but it turned out to be an effective way to fix these.
-Once pinned, quickly machine sew along the line with a straight stitch at the longest length (technical term: "basting"). Or do it quickly by hand.
-Take out the pins and try them on with the right side out to make sure they fit how you want. If they're not good, just turn them inside out and pin/baste them again until you're pleased.
-Once you have the fit you like, sew them for real. I used a double thick stitch for super reinforcement. A straight stich with a zigzag stitch next to it, or two parallel straight stitches with a shorter stitch length would also work well. If sewing by hand use very sturdy thread. Dental floss is an excellent choice because it will never break. You don't even need to sew it that neatly for dental loss to do the job well.
Step 2: Done With That
Step 3: Hemming the Legs
-Once you find the height you like, safety pin them in place on either side of your ankle.
-Take them off, turn them inside out, and iron the fold flat. If you don't have a regular iron you can use a hair iron (flat iron or curling iron. A crimper is pushing it but would likely work too.)
-Cut the extra part of the pant leg off, leaving about 1 inch. Fold the raw edge behind the extra fabric, getting the raw edge positioned as close to the ironed down fold as you can. (If this is confusing look at the hemmed part you just cut off. It should look like that.)
-Iron it in place again and sew it down flat using a sturdy straight stitch. If sewing on a machine, be careful when going over the seams, as they can become very thick and break your needle. Sew these parts at a very very low speed, or just move the needle by hand. It's also ok to skip these parts if it's that thick.
Step 4: Those Pants Look Great on You! +extra Optional Alteration
At first I thought I'd want to adjust how low the crotch is but for work pants I don't actually care. They look fine this way, I'm just used to crotch-hugging women's cuts.
(But a simple way to raise the crotch height and also do alterations at the hips would be to move the waistband. Pop all the stitches that hold the waistband down, cut the top of the pants lower, including the zipper, and sew the wasitband back on, being careful near rivets, zipper teeth, or parts where the denim is especially thick. The new top of the pants might be too wide- you can also make it narrower by taking it in from the sides before sewing the waistband back on. Make sure not to sew your pockets closed! You can also do the hip alteration without putting the waistband back on. This is especially easy if your pants have a button fly. For zippers, just remember to sew something over the zipper teeth or fold the zipper teeth at the top and stitch it down. Now the pull won't slide right off when zipping those pants.)