It kind of depends on your level of ability and of your sprint training has ever had volume in it.
If you are like a high school 100 kid that rarely does any volume. You may want to start with like a 10 in 10. Where you do 10 100s on the minute. So like 13-15s then 45-47s rest.
I usually start my 400 runners with 8*200 on the 2minute. First time they will hit around 35s, but work down to 28s. Then slowly start getting them faster or adding volume.
I really like a 3*(4*200). Where you do a set of 4 200s on the two minute and each one in the set needs to be faster than the last. So like 34, 32, 30, 28 for each set. I usually have guys try and rip the 12th on as fast as possible (had some 24s last week).
If you have two buddies (or 6) you can do a continuous 4*200 relay. So your rest is the other two legs run if you want something with a little less rest but fun. If everyone does 4*200 it becomes a 1200 relay.
I know a lot of this talks about 200s but you can do similar stuff with 100s on the min, 200s on the 2 min, 300s on the 3. Or a combo. Octoberish will have some tempo days with something like 3*350, 4*250, 6*200. Each set and rep getting faster.
PS. Most my team is 200/400 or 300mh.