Ordinary Steels/ bronze/ phosphor-bronze about every 3 weeks - but if you have bad "acid finger" every week or every gig.

Elixirs - about every 3 months - really works, saves money and hassle, and I like the sound too. I prefer nanoweb to polyweb (thinner condom).

If you want to clean strings on the guitar, and don't want to use a proper string-cleaner use a liquid degreaser. Do not use a polich it will leave unwanted deposits. Do not use an abrasive like a cream cleanser, it will leave grit in the windings. The long obsoleted Ajax ammonia plus liquid was good, my late wife used to use it in the 70s. Mr Muscle kitchen or bathroom or window would probably be good.

To protect the guitar, flatten supermarket carrier bags and thread them between the strings and the fingerboard/body. The bits of the strings by the body will not be so claggy because they don't get grease squidged onto them by fretting fingers.

UK chaps, if buying strings in bulk from USA - if they really come from USA and the customs price is over £ (not $) 30, you will (probably but not always) get hit for VAT and the fee that the post office charges for collecting it. The customs price in theory includes the shipping but often shippers do not include that.

Some US sellers used to despatch from the Channel Islands or a UK depot to avoid the VAT problem. How they got the strings to there without getting taxed on the way in I don't know.

I really think that Elixirs and changing at three months is probably cheaper than $2 string sets changed every 14 days, and is a lot less hassle, and some of those $2 string sets are truly horrid to listen to - thin and tizzy.

There are some other coated strings out there now. I'm going to try them next change. I saw some pretty coated multicolours on ebay the other day. I have tried the D'Addario coateds and they went dead for me just as fast as uncoateds. I have tried Newtones, and they suit some guitars better than others and mine seemed to be among those they didn't suit. They seem to last longer than ordinary strings but less long than Elixirs, for me, and they are quite reasonably priced.