I think the hardest thing about making miniatures, especially when you are starting out in the hobby, is getting the scale right. Figuring out just exactly what 1:12 or 1:48 or half scale or 'dolls house for a dolls house' scale really mean.
I remember when I made my first Fimo cauliflowers for my 1:12 scale kitchen. I spent ages getting the Fimo the right blend of greens, and thin enough for the leaves, and arranging them into a realistic shape. I thought it was a pretty passable effort, until I put the cauliflower on the dolls house bench. It was enormous! Not in the right scale at all.
Then I overcompensated and made things too small. But after a while I got my 'eye' in and could judge the right sizes.
One thing I have found very useful is to keep a 6 inch ruler in my handbag. Then when I'm out and about and find a miniature treasure, I can instantly measure it to see if it's in the suitable scale for my project.