Here's a little tip I've been forgetting to post.
When you're remodeling a house, always use Ctrl+Click to remove the existing wallpaper/flooring. Don't just paste it over. The reason? Simple. You save money, and can even make some.
An example:
You make a 1x4 piece of wall and cover one side with a wallpaper that costs $2 each. You then decide against it and replace it with the same amount but it costs $1 each.
If you pasted it on, you spent $3 per segment, and $12 in total. However, if you removed it first, the game would refund part of it or all of it, so it would remove maybe $1 per piece. You go on to place a $1 per piece section on it. Therefore, you spend $2, get $1, spend $1, meaning, in total, you spent $2 per piece, or $8 in total.
This is a handy little exploit, useful when you're starting out, or if you're frugal and like to save your simoleans to buy stuff like better beds. Sometimes you still end up spending money, sometimes you may MAKE money, and sometimes, it's free to do it.