There are quite a few factors that figure into the desired final result due to each person being so different. Generally, I would look at:
1. Wearing bottoms that actually FIT you. None of this baggy nonsense that has been going on for far too long (especially in America). That's fighting a losing and highly unnecessary battle. For the desired effect you're seeking, your trousers and shorts should be contoured to your actual measurements. No "next size up" to be safe. They don't have to be super-tight either -- think 1960s form-fitting or European styles.
2. Exploring what kinds of underwear flatter your bulge. Conventional briefs won't really work, as they usually just pull across and flatten the front. Consider brands that
- are ergonomically designed (e.g., Ergowear, 2Xist, C-IN2, Andrew Christian, Unico, Obviously).
- use "pouch engineering" (pouches that lift up and out -- Separatec, C-IN2, AussieBum, N2N Bodywear).
- have extra "assistance" such as built-in cockrings (e.g., N2N Bodywear, C-IN2, Andrew Christian).
Such styles will help much more. (I personally freeball for the most part.)
3. Using cockrings to help plump things up.
4. Figuring out what materials work best on you. Look at mesh, nylon, blends with Lycra, thin cotton.
5. Avoiding excess layers, especially those athletic shorts with inner linings (cut them out!). Opt for single-layer sport shorts.
6. Learning to be confident about whatever bulge your sport!