What are you planting and what is the ground like where you are? If you're planting in an area that has grass and weeds, you'll need to get rid of them - tilling actually isn't great because it doesn't get rid of the grass/weeds, it just breaks them up and leaves them in the ground. You'll be pulling weeds for years. I've found the best way is to strip the sod off first. If the soil underneath is soft enough to dig holes in with a trowel or shovel, that's probably fine for most plants. While nice soft, fluffy soil is easier to work in, I've found that most plants don't need it - they're pretty strong when it comes to putting down roots.
You might want to get your soil tested to see if it needs any amendments. You can get a soil test kit at your local nursery, or if you have a county agricultural extension office, they'll usually test if for you for free - plus they're usually pretty good about coming out to your place, and giving you lots of great advice as to what to plant, where, when, etc. The country extension officer can be a very valuable asset for home gardeners.