Your strategy is similar to mine (I'm predominantly an Eraser player). I tend to avoid purples completely unless they're in groups of three or more on the track, and if I pick up any I erase them as soon as I can. Focus heavily on blue and yellow (I assume you're talking Pro and not Elite) - if you avoid all but these two colors, you'll make huge combos. Get reds too, obviously, but your focus should be on the blues and yellows.
Also, whenever you see a black/white block, grab it and do what you can to get it to the bottom. You should try to get rid of the blocks beneath the black/whites by getting combos, but erase if you need to. Also, if you have any blacks in your grid, avoid paint powerups unless you have the opportunity to get a Match21 immediately afterwards, or you have a lot of blocks on your grid and the paint is red or yellow - typically, these will result in a larger payoff than if you let the blacks/whites fall.
Don't rely on paint powerups. You should always try to make matches on your own. The paints are nice, but don't make a habit of grabbing them whenever you see them, unless they're red/yellow, or you REALLY need to clear the board (i.e. it's the end of a song and you want Clean Finish).
If any one of your columns starts blinking, you gotta kinda develop an eye for the right color to erase. For example, erasing the most dominant color in the column isn't always the best solution because you may end up erasing a bunch of other blocks in your other two columns that could lead to a nice combo. Consequently, you should try to erase a color that will result in blcoks coming together to make a combo. That way, you get the most points.
Also, I believe chaining applies to all puzzle characters, so try to keep what kEn says in his tutorial in the back of your mind.
As a final note, practice with a Mono character. It sounds weird, but if you get good with Mono Pro, or ideally Ninja Mono, you can use what you learn in those modes and apply it to Eraser (and all other puzzle characters). If you can kind of start to think of purples (and in Elite, blues) as the gray blocks in Mono, it'll be easier to only collect certain colors. Eraser's really forgiving because even if you mess up you can erase the color that you didn't mean to get, but it'll make it easier if you learn to just not collect those colors in the first place.