The WW1 service records are a bit hit and miss but you may be lucky. The ones that survived (about a third) are on microfilm.It's really easy - you look up the name in a book which tells you which bit of film to look at, get it from the drawer yourself and then just spool through (more or less) alphabetically until you get to the name you want. There may be a few with the same name but with regiment/number info you can soon spot the right one. Sometimes there is only the original attestation paper from when they enlisted which gives basic info of address, next of kin, birth place and apparent age (not always true!). It may also list where he was sent and on what dates, any medals etc. Sometimes it lists any bad behaviour which can be interesting. It may have copies of the death notice telegram and correspondence with Next of Kin regarding medals and return of belongings. And one I saw the other day had an eye witness account of the way someone died which was used to confirm the death in the absence of a body.
For the 1912 one you can do the same thing in another set of microfilm in the Pensions records (if he retired or was pensioned out). You could try searching online under his name at
http://www.a2a.org.uk/ (click on global search) which might tell you if he is listed there and give you the microfilm number to look at.
Or you could look through boxes of the actual original papers. Ask at the info desk and someone will be able to guide you through ordering these up. It's a bit complex and you often need to know the particular regiment you are looking for.
You could also try looking in a book called National Roll of Honour which lists a random selection of Soldiers who served (living or killed). Divided by regions in England it is held in the reference library bit. I couldn't find one of mine in the microfilm as it no longer existed but was lucky enough to find a paragraph of info on him in the book
Hope that helps
Have fun