Now, some tips on making the landscaping look more realistic:
1. 'moveobjects' on is your friend. Use it to layer flowers together to create more depth since in nature some flower patches will be more "dense" than others. Use your < and > buttons to give partial turns to plants and rocks as you place them.
2. Use the terrain tool. If you want trees, put them at a grid intersection then go raise the terrain under the tree just slightly (I often have to soften terrain after) so the tree doesn't look like it was plopped down on the land, but has roots integrated underneath as well. It lends to the more natural feel of tree placement.
3. Next is a small step that adds huge impact. Under trees, or any other type of plants, create a light dirt patch (just one quick click with the terrain tool should do it). Sun doesn't get to the base of trees and the areas around them tend to have far less grass, especially near visible roots.
4. The game adds shadows to outdoor furniture, but regular use kills some of the vegetation underneath. Again a quick tap of the terrain paints adds this illusion. This is true around the base of your building too, especially at corners, it blends the building into the property instead of having stark contrast between walls and grass, it helps to make it appear as though it's always been there and isn't "floating" on the lot.
5. It may sound quirky, but I like to decide on who will be living there or using the property before I start to landscape (or decorate) since that may impact what they might have in their garden, how the hardscape will be placed, and so forth. A young professional in a modern home may have rocks lining the flowerbeds with minimal greenery, where an older couple preparing for retirement may have a more casual garden with lush flowerbeds lined with mulch. Explore terrain paints and keep the style of the house in mind when selecting plants and determining how structured the landscaping should be for that lot.
6. Landscaping is more than terrain paints and plants. Look around at your neighborhood and you'll see that a large part of landscaping, especially in backyards, is furniture. Outdoors is just another room. It needs lighting, decoration, and furniture (benches, chess tables, fire pits, statues, fountains, lawn gnomes, etc).
7. Hide your foundation. I'm not saying to completely line the area where wall meets ground, but I am saying to break up that line with some greenery or flowers. It adds character to the property, but it also adds realism to the lot.
I hope all of this helps.