Some obvious tips I worked out from my first attempt...

Remember, you're always going to use the = sign, which gives two approaches for your "first go" at each puzzle.

#1: Include it in your first line of guesses - two from the end or maybe three from the end would probably be favourite - to get that gratifying "green square" feeling if you're lucky..

#2: Don't include it in your first line of guesses, which gives you a space for one more number/sign guess.  You can add it on your second attempt.

It's not all single numbers.  Suppose you have a 1, a 9, and a 2.

That means they could be used as three individual numbers 1, 9, and 2. or they could be used as 19, and 2 (or 1 and 92, 21 and 9, 92 and 1, etc.) or even 192.

Ignore me, that's mostly bollocks. 

Took 6 tries and didn't get the answer. How do I find out what the answer was lol

Aaaaargh 

Always looking for the easy path me