How to create great interior design ideas for a house?

I go to garage sales, swap meets and second hand furniture stores.

Is there an app for that?

Consider learning how to draw plans. This is relatively easy now that we have computers.

I see! Yes I have tried a select few of garage sales although I haven't had much luck. I guess it is just luck of the draw.

I will keep trying. Thanks for the tip.

This has been of interest to me for a while - Do you recommend a particular website/ piece of software?

No - for the reason that I'm a retired landscape architect (who has also done some remodelling) and my business partner and I both liked hand drafting everything. I'm a long time painter as well. I wasn't a natural artist, I just liked copying cartoons once in a while as a teen. In my twenties I took a beginning drawing class and I got hooked on learning more.

I didn't learn design until my forties, but again, once I had a class in Elements of Design, I was hooked.

Now of course there is a lot of information available online, and lots of programs or tools to help anyone interested but I haven't investigated which is better or best.

If you just want to start to fool around with a pencil, eraser, a ruler, and paper, consider going to an art supply store and getting some grid paper; I'd recommend a pad of 1/4 " paper to start, maybe the 17" x 22" size pad. Oh, and you need a measuring tape, to measure rooms and the items you may want to arrange.

It's fun.

Think knowledge how to sketch plans. This is moderately simple now that we have computers.

If you want something really great for your house i think hiring the professional interior designer will be good.
Secondly considering the requirement of house members, design should be such that it give the ease feeling to the people living in house.