Buying reusable products or reusing things before throwing them away can greatly lower your waste production.
Instead of using single-use water bottles get a stainless steel, glass, or BPA free plastic reusable water bottle and make sure you use it.
If you like using straws get an acrylic, metal, or silicone straw to use instead of disposable straws. You can buy collapsible metal or silicone straws that you can bring with you anywhere.
If you visit coffee shops or get to-go coffee every morning before work ask your barista to fill your own reusable travel mug instead of using the disposable cup they provide. Some shops such as Starbucks give discounts for using your own cup.
Don't use any sort of plastic bag. Use canvas or cloth for your groceries and produce. Use reusable silicone bags instead of sandwich or snack bags.
If you have leftovers put them in reusable containers or cover them with a beeswax food cover instead of plastic wrap and aluminum foil.
Reuse old school supplies. Unused paper in notebooks can be ripped out and used as loose-leaf paper. Pens, pencils, markers, crayons, etc... can be reused or donated.
Buy second-hand clothes, furniture, decor, etc... and donate anything you don't use anymore as long as it is in good condition.