u just need to collect all the gold asap, the longer u take the faster the enemies get so the harder they are to avoid
make use of the digging to trap enemies or to reach levels below u, and thats about it
tips would be
make a point to grab the gold at the top of the screen sooner than later as when u kill an enemy they spawn at the top of the screen, and if u leave the top ones the monsters would have started to pickup speed and you'll have to kill them more often and they'll just constantly get in the way
other things are, when u kill them shooting is usually easyer but sometimes u want a delay so they don't respawn as quick so then u trap them in a hole instead, so its not always good just to shoot them
when u play a level a few times you should find some bits of gold are harder to get than other eg might require a long fall which means u could land on an enemy if they are to close, u treat these areas the same as the gold at the top of the level, get them first
if your up for a challenge and u use mame grab lode runner the dig fight and play in 2 player coop mode, probably the best 2 player version of lode runner ever made, working out how to do each level can be quite hard