Some thoughts for for a new gardener:
Keep a journal. It doesn’t have to be fancy. I received a wonderful garden journal as a gift, and it has provided insights, occasional entertainment, and perspective. I go through spells when I use it, and long stretches where I don’t. Â But it can be helpful to read about past gardening challenges, weather patterns and their effect, or which plants flourished and which failed. It also helps keep an inventory of what you planted, when, and where.
Journaling can be done with photos. Compare the photos below from two summers: 2005 and 2015. This was a bed I would re-design over and over in the early years, when I was a new gardener.  Straight lines evolved to curves.  Time can help, or it can get away from you — then you realize how much things have grown and certain plants are “taking over” and getting a run of the place. Photos can show you the plain truth.
  
Another great piece of advice I received:  Start with good foundation plants — these are  plants that add “bones” to your garden, winter, spring, summer and fall.  It’s harder to retrofit them later.  These sometimes tend to  be larger items within your planting scheme — shrubs, or small trees — so plan enough space for them to grow.
And don’t forget fences and hardscaping as a key part of your design.
Last, but not least: Â take time to smell the flowers!