Don’t try to run before you can walk!

How many parents have said that?  It is also applied to learning any new skill.
If you haven’t tied your shoe-laces properly, walking or running could be difficult.  I had great difficulty learning to tie mine – in the end my mother taught me a method I could manage, but didn’t stay fastened.  I know now that it is best to tie a simple knot, make two loops and tie them together twice.  And if the laces are still hanging down, tuck the ends under the bars made by threading them.  (See photo.)
My shoe-laces.Shoe-laces
Some time ago this rhyme came into my head.

Children who won’t tie their laces
Sometimes fall flat on their faces.

Mind how you go! and
Take care!
mean much the same.  I have heard that the latter is taking over fromHave a nice day!”  It is perhaps less likely to rankle with someone who is finding life difficult.

Watch your step!
can refer to your behaviour, as does Don’t overstep the line/mark!

One of the schools I attended had a few rules, which were enforced by staff and prefects.  On the way into the assembly hall, which doubled as a gym, there was a black line painted on the floor.  Each morning on the way to “Assembly” (as our whole school morning worship was called), we had to step over the line.  Beyond it complete silence was expected.  (It worked!)

You have to know where to draw the line.
This is not about art and design, but about setting limits or boundaries.

Walk tall!
really concerns self-respect, which term has gained popularity more recently.

Press on regardless…
…it isn’t obvious whether there will be a successful outcome or even if we are heading in the right direction!

Handle with care!
is a label on a parcel, which some people would benefit from wearing.

Don’t touch!
This instruction used to be placed everywhere in museums and National Trust properties, for example.  The Science Museum had one area where there were handles to turn and buttons to press.  That has perhaps led the way for museums to become more “hands-on”.  In some National Trust properties a teasel on a chair gets the message across, that it is not for the public to sit on.

Keep off the grass!
Like ancient fabric and wallpaper, grass wears out if too many people walk on it.

Don’t take it lying down!
and
Don’t be a doormat!
are instructions to Stand up for yourself and not let people insult you or walk all over you.

Be on your guard!
Watch out for danger and enemies, like someone guarding sheep or property.

St Paul uses this in his 1st letter to the Corinthians Chapter 16 verse 13Be on your guard.  Stand firm in the faith; be men of courage; be strong.