To make your writing more legible remeber that it is being written for reading later. Illegible writing is awriting which cannot be read. So the only thing to be remembered while writing eachletter and word is that thr formations should be correctly and completely made.
If you just thread along you will make waves of ink on paper. If you just skip some letters it will not be understood.
Letter a written incompletely by leaving it open from top will make it letter u.
u written with an angle instead of curve will make it v.
v written with a curve instead of an angle will make it u.
t without a cross bar will make it letter l. In illegible writings w look like m and m look likew
also n look like u and u like n.
In a hurry, the formations get wrong and in effect the whole handwriting becomes illegible.
Zones The handwriting has three zones. Upper zone is seen in letters like l, b, d, h, k, t
Lower zone is seen in letters g, j, p, q, y. If the zones are not well formed your handqriting will become illegible.
Imagine letter h without the upper zone. It will look like n. Letter d without upper zone stroke or letter g without a well formed liwerzone stroke will look like letter a.
In addition to above cases if you also do Scribbling, overwriting, using shortforms etc itmakes the writing more illegible.
As a thumb rule. “Remember that the handwriting is for communication and it should be understood on reading.”
That awarenessitself will give you a motivation to write legibly.