For oil pan gasket I think the biggest "key" is to make sure the oil pan gasket surface is straight. Most of them are out of shape from the bolts being tightened over the years, or overtightened. You'll need to straighten the gasket surface first and foremost. Use a torque wrench when tightening them again. You'll be amazed at how little torque it takes for these.
After scraping the gasket surfaces, I like to try and remove any previous gasket glues with some lacquer thinner and rag.
I've used Gaskacinch, Hi-tach, and a few others with good results. Gaskacinch seems to work well and removes fairly easily too. Although there are places to use for sealing with these products, I try to use these products sparingly and to keep the gasket in place, not to seal. That is what the gasket is for.
