Here are a few trade secrets for easy fillering...
1) Never try to filler too much at once, do it in stages or you will get shrinkage cracks!
2) Use a decent filler knife and a plastering trowel, hold the trowel against the area to be filled and push in with the knife
3) Use a sanding block and sandpaper to get a flat surface
4) Easi-fill filler can be bought in 10kg sacks very cheaply and sands very easily, some DIY fillers are not sanded easily at all!
Allfix Ltd 01202 519066
If these tips fail adopt this phrase instead...
'If the job is worth doing well it is sometimes better to get someone else to do it!'