Landscape design has many factors to consider - line, color, texture, function.
I start with function. Want an outdoor gathering place? Want lots of flowers to cut and bring indoors?
"Hardscape" comes first in layout. This is the permanent structures like pathways, patios, fountains, etc. Remember that trees are permanent too. Making a diagram/drawing on graph paper helps.
Then you get to choose plantings- location and type. Consider how much time you want to spend. Some plants are high maintenance, while others, like iris, are easy. Consider annuals that require planting each spring vs. perennial. If you're wanting something in bloom at all times, read the info that comes with each seed pack/transfer.
Many nurseries give classes. Check with your local garden center. Students often get discounts on purchases. :) You can also search "landscaping design basics." You'll find a multitude of sites and apps.
