It is very easy to think that some people have bumps and some do not. Nobody enjoys bumps so there must be a way out. Here is what I have found works;

Exfoliate the skin in the area you want to shave 24 hours before shaving to remove any dead skin cells on the surface
Dampen hairs in the shower only briefly prior to shaving
Apply shaving cream or gel — not soap — before shaving. Shaving creams and gels are formulated with agents that make the skin slippery and help the hairs to fluff up. This allows you to shave with less pressure, and to avoid scraping the skin, which risks deep nicks, but also causes microscopic cuts, roughness and inflammation of the skin. This swelling of the skin may close off the follicular openings, causing the hairs to get stuck beneath the surface, which results in razor bumps
Clean all your razors with hot water and alcohol before and after use. Discard razors after they’ve been used for one week
Shave the bikini area in the direction of the hair growth using a sharp, single-blade razor to avoid shaving too closely — a close shave means that the hairs have settled further beneath the skin surface
Apply hydrocortisone cream at the first sight of a growing red bump. Spot application for a few days can reduce inflammation and break the cycle of an ingrown hair forming, but do not apply it daily because it will cause skin damage and stretch marks if overused.
Don’t shave daily; this will give the skin time to heal
If you regularly feel itchy after shaving, make sure your shave gel or cream is free of irritating fragrances and mentholation
Wear looser clothing the first day or two after shaving to keep pressure off the involved areas
Do not wear heavy makeup on your hair bumps. This will only cause more skin irritation