+4 C for short tem storage (1-2 weeks) and -20 fC or longer time will be Ok

you can store at -20°C.

Genomic DNA usually at 4 degree (even long time) since you will otherwise break it during freeze and thaw procedure.

For permanent storage, I recommend you to precipitate with ethanol and dry-up completely, then close the tube completely with paraffilm and store at -20°C. Replacing N2 gas before closing is better.

For working storage, I agree with Sa-fa and Adrian. You should prevent frequent freeze-and-thaw which would cause DNA unfortunate shearing in the case of big size DNA such as genome.

Very good points indicated by Nor!

It is a common question that come in our mind. I suggest you to keep the DNA sample in -20 C for long time storage. When you'll use it, place it in 4C before 1hour of your work.