I can tell you what helps get me boned up. When i put on certain jockstraps, a "viagra effect" takes over. The way the pouch cradles my genitals, the way the straps grip and frame my ass, jockstraps cause me to sport pretty good bulges.
Either that, or perhaps another type of sexy garment can help.
Then there's always mental imagery or how mental scenarios can excite you enough. When the masseuise paraded me out of the room toward another room to show me off in my jockstrap, that made me bone up too, knowing i was on display.
Then of course, there is that light, sensual caressing. Softly having someone's fingers, or even long hair, sweep over your whole body at varying speeds while you lie face down, occasionally reaching underneath.
So you can experiment with touch, with clothing, what turns you on mentally, whether you can imagine or try to live the experience. These are all things that can help.