If you are going to bottom and usually find your tops too quick on the insertion / are worried about your top going in too quickly or you're a top worried about hurting your bottom, try this:
Have the top sit down while maintaining his erection. Make sure to lubricate it (with water-based lube for latex condoms).
Next, have the bottom gradually sit down on the erect dick. This can take some time for inexperienced bottoms as they learn to adapt to the sensation of having a dick in their ass. Make sure the bottom stops immediately once he feels he's about to take on too much; that's a clear warning sign that his ass needs to get fully adapted to the dick before taking on anymore.
The bottom could withdraw his ass (it feels good, a nice relief from the stress of being penetrated), but that doesn't progress its adaptation for the top's dick.
Eventually, the bottom's ass gets past the head, which is often the broadest part of the dick. Even then, it's important to be aware of whether his ass is taking on too much; ultimately, you may reach a point where his ass can't take on anymore, whether due to anatomical limitations (not all guys can take on a nine-incher) or uncleared bowels (which is why douching / enema use / a high-fiber diet is important).
Once the bottom's ass has adapted to the dick, it should be ready for fucking (in a variety of positions). Make sure to add lube according to need or want, as it wears off, which can lead to unpleasant friction. Don't think of it as lubricating the dick, but keeping the inner ass lubricated for the dick.