Before picking a slot game, three things need to match: volatility, RTP and the ratio of minimum bet to your budget.
Volatility or variance tells you how often and how large a win can be. High-volatility games like Nolimit City's Fire in the Hole xBomb can go through long dry spells, but when a win comes it tends to be large. Low-volatility games pay out smaller amounts more frequently, which suits longer sessions without a large balance.
RTP is the theoretical long-term percentage of every ৳100 wagered that is expected to be returned. PG Soft's Fortune Mouse has a maximum RTP of 96.96% — this number is not a guarantee, but it is a useful reference.
Budget and bet size: it is wise not to place more than 2–3% of your session budget on a single spin. This gives you more playing time and increases the chance of hitting a bonus round.