There are many ways to do a waistband and a particular favourite of mine is the elastic back with a flat front.
I find Miss 13 likes this style and wears it in many of her skirts & skirt style shorts.
It can also help with not having to add any closures to some of your garments.
1. Take your back piece, fold a 5mm hem and then fold waistband over as per pattern or at least the width of your elastic.
2. Thread through your elastic
3. Secure the ends of the elastic with some baste stitching
4. Sew your back piece to the front - matching the fabric from the bottom hem. You will be left with a front flap at the top as shown.
5. Trim your elastic back, remove basting stitching. Press your seams towards the front and press over the side seam of the front waistband flap
6. Again press a 5mm hem along the front waistband edge and fold over to match the back waistband stitching. Sew your final row of stitching along the front waistband.
NOTE: If you are adding this style of waist to an existing pattern, as with all altering of patterns, you need to consider how the changes will effect the finished garment. Do you need to reduce the front panel sides if the pattern original pattern allowed for an all elastic waist? Is the back gathered enough that the garment can be taken on and off easily without a zip?
In my example, this is an A-Line skirt which I have added the required allowance to both front & back sides.