Airlines are trying to nickle and dime you every chance they have. In addition to paying top dollar for tickets, Air Canada (as an example) charges a fee for every piece of checked luggage and is making carry-on allowances smaller and lighter.
Your only option is plan and plan and plan. Start planning your trip as soon as possible and determine what you will be doing and where you will be going. Based on your plan, create a list of what you need to bring with you (and don't start this list the night before).
The goal is to travel as light as possible with the least amount of luggage. Try to minimize your the amount of clothes you bring by ensuring you can mix and match everything. Bring items that are weather appropriate but as light and small as possible (it may not be a good time to pack that thick and heavy sweater that weight 12 lb).
Try to limit the number of inflexible space consuming items like shoes. Years past, I use to carry my toiletries in a thick, resistant leather toiletry bag but it just weights too much. I now carry my toiletries in 1L Ziplock style freezer bags (freezer bags are thicker and more spill resistant that cheaper "normal" plastic bags).
When possible, I encourage to travel "carry-on only" (OneBag) and my favorite luggage is RedOxx brand (lifetime warranty, light and super durable).