On level 1, allow all of the enemies to appear and
fly into formation without shooting any of them.
After the boss alien appears (the one that carries
the tractor beam attachment), you'll see a pulsar
similar to the ones the aliens appear from fly from
just above the boss alien to the middle-right of the
screen. Once it's gone by, shoot only the second alien
from the left in the bottom row of the formation.
A "Special" flag will appear just below where it was;
pick it up and you'll get a bonus ship.
In Parsec 1, go up to the very front and wait for all the
bugs to come out. Then kill the 2nd bug from the left in
the bottom row to make the special flag appear. Now, when
the boss is coming down, move your ship and kill yourself
by touching it. Don't touch the blaster head, just the
boss. Your ship is turned into the blue one, and go get
the special flag.
Another approach to the same situation:
At the start of the first round, push straight up until
you stop. DON'T shoot! Just sit there and let all the bugs
form. Right after the last row of bugs get into formation
a star will shoot from the top left side of the screen to
the bottom right. If you time this right you can get up to
5 shots on it. After about 10 hits on the star (it will
come out at random times during the game) it will transform
your ship into a new ship that can shoot 3 shots on the screen
( 3 shots verticaly in a row ) instead of just 2.
There used to be a book called "All about Namco" in
Japan years ago which included the tips, maps, and
everything of all Namco games. It had a few pages about
Gaplus and there was a table showing which bug you need to
kill to get the special flag. I don't remember exactly how
it goes, but it was kinda like this. If your score's 1000
and 100's digits are 00 when the new parsec begins (for
example, when your score is 0000, 10000, etc.), you need
to kill the second bug from the left in the bottom row.
If those 2 digits are 01 like 10100 and 20100, kill the
3rd bug from the left in the bottom row, etc. 03 is the
4th bug and so on. I think it goes all the way to the most
right one in the bottom row, then the 1st one to the left
in the second bottom row. When it gets to the most right in
the second bottom row, it comes down to the 1st one to the
left in the bottom row, then you're back at 00 (2nd bug just
like parsec 1).