If you are going below 4 it could be because your basal is too high. Of course, working (especially if physical) will tend to make your level drop more than usual, so if you were taking rapid insulin during that time you would need a bit less of it.
I take my basal before I go to bed because I want to make sure it's working overnight when I can't check my levels and take remedial action manually. If you take it in the morning then it might not be fully working overnight, because although it lasts 24 hours in theory, in practice it can 'run out' before then.
The first thing to do is make sure your fasting level is on track, ie. below 7.8 but preferably more like 5-5.5 at most. Mine is usually between 4 and 5. I wouldn't encourage someone just beginning to fine tune their numbers, to aim to be too perfect because you do want to avoid, or at least minimise, hypos (going too low) as they can be potentially dangerous of course. So make smallish adjustments to begin with. But you must take into account what you're eating and adjust your rapid insulin accordingly.
For example in my case, needing 1 unit of novorapid per 10g carbs:
If before a meal my blood sugar was 5, and I was to eat 50g of carbs, I would take 5 units. For me, I would take this about 15-20 minutes before eating, because for me, that works better than taking it when I eat. They call that pre-bolusing. This is not the same for everyone so you would find this out by trial and error. I would then expect my blood sugar to be back down to around 5, within 2-3 hours. Sometimes less. It depends on what you've eaten and your level of physical activity etc. but it would get you there or thereabouts and that's all that matters, it doesn't have to be absolutely exact and perfect every time.
Now say my blood sugar before eating was 7. I would add a correction dose of 2 units so I would take 7 units for the 50g carbs.
Likewise if my blood sugar was only 4, I would take less insulin, so say only 4 units for the 50g. I personally always aim to keep my blood sugars around 5. Sometimes they will go into the 4s, that's fine, it's a very good and safe level, but aiming for 5 gives a margin of error.
This is all pretty simple really and I think most diabetics should be able to get the hang of doing this, but sadly, it seems rather a lot of type 1s have bad control, which worries me because it needn't be that way.
The other thing I do is always check my level before I go to bed, which will be 2-3 hours after I last ate anything. I will then always take remedial action as necessary, to make sure my level is going to work well for me overnight. If it is 7 or above, I will take a bit of rapid insulin to lower it. If it happened to be say 4, I might eat one biscuit (10g carbs) to raise it to 5.
I think some people probably don't do as much as I do, and leave things to chance. With diabetes I don't think that's a good policy.