Well, a 260 litre (or 65 US Gals) tank is not a bad sized tank.
The question is, what fish do YOU like?
Have a look at your LFS and write down the names of the fish that you like the look of. Then come back here and type them up.
But with one condition, you must let us know what your water is like, what we need to know is, what the pH is for a start, then is it hard or soft water.
You'll likely find the hard / soft water from your local water supply online, either copy or do a screenshot of something like that and post that here. We then can see what would be suitable.
There are many fish species out there, so we need out work out if they will thrive in your water conditions, not get the water condition to suit the fish, much harder than it sounds to change water parameters.
Then we can see if these species will be compatible with each other, in terms of aggression or territorial species or if they will grow too large for your tank.
For example, Betta Splenden do best in a tank of their own, usually a5 to 10 gallon tank is best, they would be lost in a 200 litre tank.
But Clown Loaches, they are a social species and like groups of at least 6 of them but they need a big tank, at least 6 feet long.
That is just two example where its very easy to get things wrong and will be potential problems later on, so its always best to research first or ask the more experienced keepers what they think.
Glad youre asking before you actually bought any fish
By the way, is this a new tank?
And one last point, is this tank already cycled?
If not sure what cycled means, have a read -
Cycling Your New Fresh Water Tank: Read This First!
NOTE - forgt to ask, would be of a good help if you can give the dimensions of this tank, length x width x height .
PPS NOTE - just noticed you have started another thread and you have some fish already, are these fish in this tank already?
Can you list your fish species here and how many of each you have.