The best way is to keep a tin of machine oil, a small tin is cheap and will last a long time. Clean and wipe your tools dry after use then wipe a light coat of oil on them. All my tools are years old and still going strong.
A rub with a fine file will put the edge back on Secateurs, there will be a flattish edge on the blade just before the cutting edge so rub the file from the back of the blade towards the cutting edge taking off any burrs. Then take a spanner to the centre nut and bolt and nip it up until you feel a little pressure as you press the handles together. Give them a good oiling and hang them up, it is best to hang all tools, you know where they are and they are not lost under a heap of something.
A lawn mower blade can be sharpened the same way, run a fine file from the back of the blade to the cutting edge in circular sweeping movements, you will get the hang of it after a few runs finish with a bit of fine sand paper and oil, I even oil the wood shafts of all my tools.
Hope this helps.