It's a 1.4 n/a so big gains are near on impossible unless you pump serious money into it.
To keep things sensible, go for a decent exhaust system, spark plugs and pannel filter. Pannel filters for the 85 are rather hard to find as I previously ordered one via two different companies and I had the same issue so gave up in the end.
Apart from that, upgrading the suspension won't give you more power but will give you better handling effectively making you faster through the corners.
If you decide to go for the pannel filter, heres the one you need for the 85 1.4 engine:
http://www.knfilters.com/search/product.aspx?Prod=33-2920
Good luck