Actually there's only a bit of luck involved, hence why it's possible to make a website like that. I make it to level 5 or higher most times I play (and I don't use the website, because it's too slow). The main thing to remember is that you advance when you reveal all of the 2-tiles and 3-tiles, so the 1-tiles are almost as bad as the Voltorb ones.
Some general advice:
1. If there are no Voltorbs in a row/column, flip all the tiles over.
2. If the number of coins and Voltorbs in a row/column adds up to 5, you should mark all of the tiles in it, because it only contains 1-tiles and Voltorbs.
3. In general, whenever the number of coins and Voltorbs left in a row/column adds up to the number of tiles left, mark all the remaining tiles.
4. Try to learn the possible combinations of tile numbers for particular coin/Voltorb numbers. For example, 5/1 contains a single 2-tile, and the rest must all be 1-tiles and Voltorbs. 6/3 contains two 3-tiles and three Voltorbs. 5/2 can contain two 2-tiles or a single 3-tile. And so on.
5. Use your knowledge of the possible tile combinations to work out which tiles are safe to turn over and which should be marked. For example, if a 6/3 column intersects a 5/1 row, then you should mark that tile because it must be a Voltorb. Then you can then flip over the rest of the tiles in the 5/1 row.
6. Finally, sometimes you will be forced to make an educated guess. In these situations you should aim for rows/columns with the lowest Voltorb totals and the highest coin totals, remembering to take into account tiles already flipped/marked.