Head shaving, especially with a straight razor, is not for everyone. However, if you want to try it then please read the following article.
Blade: Some find that shaving their head does dull the blade faster than shaving their face, but not all people have this problem. Before you shave you want your blade to be sharp, super sharp. For most people stropping is enough. Personally, I run my blade 5 laps on an 8k and strop 30 laps before shaving.
Lather: I use super hot water in my cup and put my brush in it while I’m getting everything ready. Once the hairs of the brush have been softened I lather up with a good soap. After that I begin to strop. This gives the acids in the lather to work into the hairs and makes cutting them easier. After stropping I reapply more hot lather just before shaving.
The First Pass: Consistency, consistency, consistency! I always start from the top right of my head working my way to the sides and next the back. Then I move to the left side with the left hand. One “requirement” for head shaving with a str8 is to shave with both hands. I would also have someone, a spotter: wife, neighbor, roommate, take a look at your head to see if you missed anything (you will be surprised!). If you don't have a spotter I know for me the hard parts to shave are behind ears and where my skull meets my neck.
Recommendation for the first pass: Always hold the razor firmly! I hold my razor much firmer when shaving my head then shaving my face. I do this because there is more hair on my head and I need to control the blade better. “Holding firm” does not mean pushing firm. Never push down with a str8, let is skim your head. I would recommend having two mirrors, so you can see your entire head. I would also suggest that you watch your saving angle when shaving the back of your head. This will lead to dulling the blade. I also take small strokes on the first pass mostly because I let my hair grow for one week before I shave, but it also helps cut more hairs. My final recommendation would be to overlap your passes, meaning; you take a pass and clear away a ¾ inch path, then your next stroke will overlap the already shaven part of your head by about 3/8” or so. If you don't overlap your passes you will wake up with a zebra patter five o’clock shadow the next day.
Second Pass: I, personally, strop before my second pass. When first starting out I would do just do a normal with the grain second pass and concentrate on the areas my spotter would find most often. After several months I started going across the grain with the second pass. This helps get all of the hairs without so much overlapping and gives a closer shave. Be careful not to go to fast or angle the blade the wrong way because shaving across the grain will bite you! Only after eight months of head saving with a str8 did I start shaving against the grain.
Against the Grain: Against the grain is not just reserved for the second pass. In fact, because of how my skin is on my head I do the top of my head ATG and the back and sides ATG on the second pass. Shaving like this gives you a great shave but be ware this too will bite you! Make sure you are holding your skin tightly with your other hand. When shaving the back of my head I put my chin to my chest. This makes the skin tight for the back. I also use more of an acute angle when shaving ATG.
Since you have survived your first shave splash your head with cold water. This helps seal the pores. There are several head shine or dull product on the market you may want to check out for you’re after-shave.